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Chemistry ATAR Y12
All of it
| Term | Definition |
|---|---|
| What is the rate of reaction and how is it determined? | The Rate of Change of the Number of Moles of Product in a chemical reaction (mass of product produced in a given time). |
| According to the Collision Theory, what three things must happen for a chemical reaction to occur? | 1. Particles must collide 2. Collide with correct orientation 3. Must collide with sufficient energy to overcome activation energy |
| What is activation energy? | Minimum amount of energy for a chemical reaction to initiate and break bonds within reactants |
| What is the difference between an exothermic and endothermic reaction? | Endothermic – absorbs energy as the reaction progresses Exothermic – releases energy as the reaction progresses |
| What does the term enthalpy mean? | The energy contained with a set of substances. Chemist are interested in the CHANGE in enthalpy during a reaction |
| What 5 factors affect the rate of a chemical reaction? | 1. Pressure 2. Temperature 3. Concentration 4. Surface Area 5. Catalyst |
| How can rate of reaction be determined experimentally? | By measuring, either directedly or indirectly, the formation of products or the depletion of reactants over time. |
| Factors that can be measured to determine include | - Mass lost by reagent - Mass gained by product - Volume of gas - Pressure of gas - Colour intensity - Solution concentration - pH |
| Orientation | Is the result of their random motion and not something that can easily be modified to increase their rate of reaction. |
| Sufficient energy | Required amount of kinetic energy for successful collision that generates products. This energy is a requirment of the bonding breaking/formation process. |
| What is meant by 'transition state'? | The highly energised and highly unstable arrangement of reactant particles where the bond breaking/formation takes place. |
| Concentration (Effect on Rate of reaction) | Number if particles per unit of volume (eg: moles per litre) Increase successfulness of collisions |
| Pressure (Effect on Rate of reaction) | Force per unit area that gas particles exert when they collide with the walls of the container. High gas pressure <- increased number of gas particles in a given volume |
| Temperature (Effect on Rate of reaction) | Increase average kinetic energy causes particles to move, on average, with an increased speed causing a greater frequency of collisions, both successful and unsuccessful |
| Catalysts (Effect on Rate of reaction) | Provide alternative reaction pathway with lower activation energy , leading to a greater proportion of the reactant particles having enough energy to overcome the now reduced activation energy |
| Describe the three types of energy system. | Isolated System – Vacuum (Neither can escape) Closed System – Lid (Heat can escape, not matter) Open System – Cup (Both can escape) |
| What does it mean for a chemical reaction to be reversible? | A reversible chemical reaction is one in which the products can react to reform the original reactants. Can proceed in both directions Often react a state of dynamic equilibrium, where the rates of forward and reverse reactions are equal. |
| What determines the reversibility of a chemical reaction? | Energy changes, reactions with small energy changes are more likely to be reversible If the activation energy for the reverse reaction is not prohibitively high, reversibility is more likely. |
| What indicates a reversible reaction in a chemical equation? | ⇄ Double arrow shows reversible reaction |
| H2O (l) ⇄ H2O (g) How does this process vary in an open system? | Open system - rate of process not equal. Gaseous water molecules are escaping into the atmosphere, so the rate of the reverse reaction (condensation) does not become equal to the forward reaction. Equilibrium is not reached |
| H2O (l) ⇄ H2O (g) How does this process vary compared to a closed system? | Closed system - water vapour cannot escape. Rate of forward and reversse reaction are equal (reached a state of equilibrium). |
| Describe the processes occurring in a saturated sugar solution. | Sugar molecules are dissolving at the same rate as they are crystallising, and the mass of sugar crystals present are constant. |
| Close systems without lids | Even though there is no lid on the beaker, the system is considered closed, as no gas is involved (no loss of reactant or product to the surroundings) See: Saturated Sugar Solution |
| Haemoglobin is responsible for the transport of oxygen of oxygen from your lungs to the cells in your body. | haemoglobin + oxygen ⇄ oxyhaemoglobin Equilibrium is established in the blood as it flows through the body. It can be thought as a closed system as there is no loss of reactants or products to the surroundings |
| What is meant by a system at equilibrium? | At equilibrium, the concentration of reactants and products remain constant, even though there are still reactants remaining (I=i.e. do not proceed to completion) |
| What types of systems can reach equilibrium? | Reversible reactions in a closed system eventually reach a situation where the rate of the forward reaction and rate of reverse reactions are equal, there is no further change to the observer. |
| Why would systems that reach equilibrium have serious consequences to produce chemicals in industry? | Large amounts of unproduct reactants. |
| Define partial pressure | The pressure exerted by an individual gas in a container, at the same temperature Dalton's law of partial pressures |
| What happens during dynamic equilibrium? (1) | Macroscopic properties remain constant - concentration - pressure - temperature Reaction is 'incomplete' and all substances are present in the equilibrium mixture (weak acids are incomplete) |
| What happens during dynamic equilibrium? (2) | At the molecular level, bonds are constantly being broken and new bonds formed as reactants and products continue to be converted from one to the other. |
| What happens during dynamic equilibrium? (3) | Dynamic equilibrium is reached by reversible physical or chemical reactions taking place in a close system |
| What is meant be 'extent of reaction'? | Extend of reaction indicates how much product is formed at equilibrium, whereas rate of reaction is a measure of the change in concentration of the reactants and products |
| Define equilibrium in a chemical reaction. | Equilibrium in a chemical reaction is when the concentration of reactants and products remain constant, even though there are reactants remaining |
| Why is equilibrium often considered dynamic? | Bonds are constantly being broken and form in a reaction |
| Can equilibrium be reached in an open system? | No as matter can escape |
| What is the difference between partial pressure and total pressure of a gas mixture? | Partial pressure is the pressure exerted by an individual gas in a container at the same temperature Total pressure of as gas mixture is all the pressures added together |
| What are the macroscopic properties of a reaction and what happens to them once equilibrium is reached? | Macroscopic properties of a reaction are concentration, pressure and temperature, which when equilibrium is reach stay constant |
| What is the Equilibrium Law and | Equilibrium constant (Kc) is the value of the concentration fraction when equilibrium is reached. |
| how does the Equilibrium Constant apply for different chemical reactions at equilibrium. | - Only has meaning when at equilibrium - Quantities the extend of the reaction - K is constant for a given reaction at a given set of conditions (temperature) |
| Pure solids and liquids | Pure solid and liquids have a concentration of 1, which allows some equilibrium equations to be simplified |
| What is equilibrium yield? | The quantity of products produced at equilibrium |
| Describe what certain ranges of equilibrium constant mean for the extent of reaction. | Equilibrium Constant Range / Extent of Reaction >10^4 / Almost a complete reaction 10^-4 - 10^4 / The extend of the reaction is significant <10^-4 / Negligible reaction |
| How does an INCREASE in temperature affect exothermic vs endothermic reactions? | Reaction Type / Effect on Equilibrium Constant / Effect on Equilibrium Yield Exothermic / The value of Kc decreases / Amount of product decreases Endothermic / The value of Kc increases / Amount of product increases |
| State Le Châtelier’s Principle | Le Chatelier's Principle states that a system at equilibrium will act to partially counteract any change imposed upon it |
| The position of equilibrium may be changed by: | Adding or removing a reactant or product Changing the pressure by changing the volume (involving gases) Diluting (in solution) Changing the temperature |
| If we apply a stress to this system by adding more N2, we can use Le Châtelier's Principle to predict the response. (1) | PREDICTION Adding N₂ will increase the partial pressure/concentration of N₂ in the system Therefore the system will respond to reduce the partial pressure to N₂ in the system |
| If we apply a stress to this system by adding more N2, we can use Le Châtelier's Principle to predict the response. (2) | The forward reaction is favoured, shifting equilibrium to the right Reducing the partial pressure of N₂ (Note: The final partial pressure of N₂ will still be higher than the original partial pressure) |
| Explain that shift in terms of Collision Theory. (1) | EXPLANATION Adding N₂ to the system, increases the number of N₂ particles in a given volume (increases the partial pressure) |
| Explain that shift in terms of Collision Theory. (2) | Therefore, the frequency of collisions with H₂ will increase, increasing the rate of the forward reaction (while the rate of the reverse reaction initially remains constant) |
| Increase in concentration | Equilibrium shifts to the right to reduce the effect of increase in the concentration of a reactant |
| Decrease in concentration | Equilibrium shifts to the left to reduce the effect of increase in the concentration of a reactant (or an increase in the concentration of product) |
| When the Stress is an increase of pressure (smaller volume) predict the Shift | System acts to decrease pressure by shifting to the side with the fewer number moles of gas The forward reaction will be favoured, shifting equilibrium to the right |
| When the Stress is an increase of pressure (smaller volume) explain the Shift (1) | Increasing pressure, increases number of particles in a given volume for all species This increases the frequency of collisions, therefore, increasing rate of reaction |
| When the Stress is an increase of pressure (smaller volume) explain the Shift (2) | This applies to both the forward and reverse reactions, but the rate of the forward reaction increases more due to the number of moles of gas involved |
| When the Stress is an increase/decrease of pressure explain what happens when there are equal number of reactant and product particles | *When there are equal numbers of reactant and product particles, a change in pressure will not shift the position of equilibrium. |
| When the Stress is a decrease in pressure (larger volume) predict the Shift | Le Chatelier's Principle states that a system at equilibrium will partially counteract a stress imposed upon it. Therefore, the reverse reaction will be favoured, as it produces are larger number of moles, shifting equilibrium to the left |
| At point of stress imposed | Partial pressure of Cl2 will halve, but number of moles of Cl2 will remain constant |
| Re-establishing equilibrium | Partial pressure and number of moles of Cl2 will increase |
| At new equilibrium position | Number of moles of Cl2 will be more than originally but the partial pressure will still be less than originally |
| Increase in pressure | Equilibrium shifts in the direction that produces the smaller number of molecules of gas to decrease the pressure again |
| Decrease in pressure | Equilibrium shifts in the direction that produces the larger number of molecules of gas to increase the pressure again |
| Explain why inert gases do NOT affect equilibria. | The total pressure of equilibrium mixture of gases may be changes, without |
| How does diluting a solution affect equilibrium? | It decreases the concentration of all aqueous species, shifting equilibrium to the side with the larger number of moles (dissolved particles) |
| Increase in temperature | Want to cool down (absorbs heat) Equilibrium moves in the endothermic direction to reverse the change |
| Decrease in temperature | Want to heat up (release heat) Equilibrium moves in the exothermic direction to reverse the change |
| What effect does a catalyst have on equilibrium? | A catalyst has no effect on equilibrium position, but it will cause equilibrium to be reached faster, as catalyst increase the rate of both reactions |
| Lavoisier | Acidic properties due to the presence of oxygen |
| Davy | Acidic properties related to hydrogen content |
| Arrhenius | Acids release H+ and bases release OH- in solution |
| Acid | Acid is a substance that donates a proton, H+, to a base |
| Base | Base is a substance that accepts a proton from an acid |
| Hydronium ion | H₃O⁺ |
| Advatnages and a limitation of Bronsted-Lowry Model of Acid and Bases | Explains gas reactions (not in solution) Explains substances such as ammonia Cannot be applied to reaction of acidic and base oxides |
| What is meant by conjugate acid-base pairs in acid-base equilibria | What is meant by conjugate acid-base pairs in acid-base equilibria Conjugate acid becomes a acid in reverse reaction Acid paired with conjugate base Base paired with conjugate acid |
| Amphoteric | Can act as either an acid or a base, depending what it's with E.G Water |
| How do we determine which one dominates in a given solution | The relative strength If the solute is a stronger acid than water, water will act as the base |
| Monoprotic | Acids donate only 1 (ONE) proton (H⁺) HCl, HF, HNO3, CH3COOH |
| Polyprotic | Acids can donate more than 1 proton H2SO4, H2SO3, H3PO4, H3BO3 |
| Strong Acid | Acids that readily donate a proton are called strong acids. Uses a single reaction arrow |
| Weak acid | Weak acids partially ionise. Uses double reaction arrow |
| Would you expect a 1M solution of HCl or a 1M solution of CH3COOH to be a better conductor of electricity? Why? | HCl as its a strong acid taht completely ionises/disociates |
| What does the Ka indicate? | Acid Ionisation Constant Strength of an acid can be described in terms of the position of equilibrium when a substance donates a hydrogen ion to water Called a Hydrolysis Reaction |
| Ka Value of Strong and Weak Acids? | Strong Acid ⇄ High Ka Weak Acid → Low Ka |
| Explain why subsequent deprotonation Ka values for polyprotic acids decrease. | A proton is being donated by an increasingly negatively charged acid species, which is energetically more difficult |
| Corelation between conjugate acid-base pairs in strength | The stronger the acid is, the weaker its conjugate base is Strong acid -> weak base Strong base -> weak acid |
| Strength | How readily protons are donated or accepted |
| Concentration | The amount of acid or base dissolved in a given volume of solution |
| Acid + Metal | Salt + H₂ (g) |
| Acid + Metal Hydroxide | Salt + H₂O |
| Acid + Metal Oxide | Salt + H₂O |
| Acid + Carbonate | Salt + H₂O + CO₂ (g) |
| Acid + Hydrogencarbonate | Salt + H₂O + CO₂ (g) |
| Acid + Metal Sulfite | Salt + H₂O + SO₂ (g) |
| Base + Ammonium Salt | Salt + H₂O + NH₃ (g) |
| Base + Non-Metal Oxide | Salt + H₂O |
| Dilution | The addition of solvent to a solution to reduce the concentration |
| In the lab, you can prepare solutions of a base of a required concentration by: | Diluting a more concentrated solution (add more water) Dissolving a weighed amount of the base in a measured volume of water (dissolve something) |
| Effect on pH of Strong Acid and Bases described | Strong acid, keep adding more water, it will get close to pH 7 but never reach 7 The progressive dilution of a basic solution will cause the pH to decrease until it reaches very close to 7 |
| Salt | Salt is an ionic compound That contains a positive ion (cation) and a negative ion (anion) other than the oxide ion or hydroxide ion |
| How are Salts formed | Formed in neutralisation reactions by a combination of an acid with a base Cation deprived from base Anion from acid Dissociation (dissolve in water) ions formed than could react in a secondary reaction hydrolysis |
| Strong Acid+ Strong Base | Neutral Salt |
| Strong Acid + Weak Base | Acidic Salt |
| Weak Base + Strong Acid | Basic Salt |
| Common Neutral Ions | Cl⁻ Br⁻ NO₃⁻ |
| Common Acidic Ions | NH₄⁺ HSO₄⁻ H₂PO₄⁻ |
| Common Basic Ions | CO₃²⁻ HCO₄⁻ SO₄²⁻ HPO₄²⁻ PO₄³⁻ F⁻ |
| Buffers | Buffer solutions (EXAM QUESTION) are able to resist a change in pH when small amounts of acid or base are added Made of either a weak acid and conjugate base or weak base and conjugate acid |
| Why are buffers important? | This is important for processes that require stable and narrow pH ranges |
| A buffer solution consists of | A weak conjugate acid-base pair Could be made from a Weak acid and conjugate base Weak base and conjugate acid |
| CH₃COOH (aq) H₂O (l) ⇄ CH₃COO⁻ (aq) + H₃O⁺ (aq) Explain what happens if a small amount of HCl is added to the system at equilibrium. (1) | Adding HCl will increase the concentration of H₃O⁺ ions in the system, decreasing the pH of the system This will increase the frequency of collisions with ethanoate, increasing the rate of the reverse reaction |
| CH₃COOH (aq) H₂O (l) ⇄ CH₃COO⁻ (aq) + H₃O⁺ (aq) Explain what happens if a small amount of HCl is added to the system at equilibrium. (2) | Equilibrium will shift to the left Therefore, the concentration of H₃O⁺ ions will decrease, increasing the pH of the system (partially counteract. pH still was decreased) |
| CH₃COOH (aq) H₂O (l) ⇄ CH₃COO⁻ (aq) + H₃O⁺ (aq) Explain what happens if a small amount of NaOH is added to the system at equilibrium. (1) | Adding NaOH will increase the concentration of OH⁻ ions in the system. (OH not present in system from beginning) This will neutralises H₃O⁺ ions in the system, decreasing the rate of the concentration of H₃O⁺ ions, increasing the pH of the system. |
| CH₃COOH (aq) H₂O (l) ⇄ CH₃COO⁻ (aq) + H₃O⁺ (aq) Explain what happens if a small amount of NaOH is added to the system at equilibrium. (2) | This will decrease the frequency of collisions with ethanoate, decreasing the rate of the reverse reaction Equilibrium will shift to the right Therefore, the concentration of H₃O⁺ ions will increase, decreasing the pH of the system |
| NH₃ (aq) H₂O (l) ⇄ NH₄⁺ (aq) + OH⁻ (aq) Explain what happens if a small amount of HCl is added to the system at equilibrium (1) | Adding HCl will increase the concentration of H₃O⁺ ions in the system. (OH⁻ not present in system from beginning) This will neutralises OH⁻ ions in the system, decreasing the rate of the concentration of OH⁻ ions, decreasing the pH of the system. |
| NH₃ (aq) H₂O (l) ⇄ NH₄⁺ (aq) + OH⁻ (aq) Explain what happens if a small amount of HCl is added to the system at equilibrium (2) | This will decrease the frequency of collisions with Ammonium, decreasing the rate of the reverse reaction Equilibrium will shift to the right Therefore, the concentration of OH⁻ ions will increase, increasing the pH of the system |
| NH₃ (aq) H₂O (l) ⇄ NH₄⁺ (aq) + OH⁻ (aq) Explain what happens if a small amount of NaOH is added to the system at equilibrium | Adding NaOH will increase the concentration of OH⁻ ions in the system, increasing the pH of the system This will increase the frequency of collisions with Ammonium, increasing the rate of the reverse reaction |
| NH₃ (aq) H₂O (l) ⇄ NH₄⁺ (aq) + OH⁻ (aq) Explain what happens if a small amount of NaOH is added to the system at equilibrium | Equilibrium will shift to the left Therefore, the concentration of OH⁻ ions will decrease, decreasing the pH of the system (partially counteract. pH still was increased) |
| Buffer capacity | Is a measure of the effectiveness of a buffer solution at resisting a change in pH when either a strong acid or strong base is added |
| Buffer capacity effectiveness | A buffer is most effective when more HA (weak acid) molecules an A- (conjugate base) molecules are available to react with and neutralise the effect of the addition of a strong acid or base |
| Buffer capacity is greatest when: | There is a high concentration of the weak acid and conjugate base The concentration of the acid and its conjugate base are equal |
| Acidosis | Caused by Pneumonia Emphysema Diabetes When the pH of the blood drops to potentially lethal level |
| Alkalosis | Causes: Hyperventilation rapid breathing increase Increases pH |
| Carbonic Acid/Bicarbonate Buffer | CO₂ + H₂O ⇄ H₂CO₃ ⇄ HCO₃₋ + H⁺ Present in blood cells Respiration in the cells produces carbon dioxide. The carbon dioxide dissolves and decreases blood pH according to the reaction above |
| CO₂ + H₂O ⇄ H₂CO₃ ⇄ HCO₃₋ + H⁺ Outline how does this system maintains stable blood pH when there is an increase in [H3O+]? | The buffers in the blood act to reduce the effect of additional acid (H₃O⁺). According to Le Chatelier's principle, the system responds to oppose the change and restore equilibrium as some of the addition H₃O⁺ produced by the carbon dixide will react wi |
| What is an indicator? | An indicator is a chemical that has a different colour in acidic and basic solutions and used to distinguish between acids and bases They are weak acids or weak bases Th position of equilibrium depends on pH |
| What is important about the acid-base conjugate pair? | The acidic form of an indicator (HIn) and conjugate base for (In⁻) are different colours |
| Adding Hydrogen ions to indicator | Equilibrium position moves to the left remove extra hydrogen (reverse reaction) Litmus turns red |
| Adding Hydroxide ions to indicator | Equilibrium position moves to the right to replaces lost hydrogens (forward reaction) Litmus turns blue |
| Universal indicator | Universal indicator is a mixture of several indicator and changes through a range of colours, from red through yellow, green and blue, to violet. |
| Bromothymol blue | The bromothymol blue indicator is yellow in acidic solutions and blue in basic solutions. In the neutral solution of pH 7, the indicator is green |
| Bromothymol blue: Adding HCl solution | Equilibrium is shifted to the left to oppose the increase in the concentration of H₃O⁺ HBB becomes greater in concentration than BB⁻ and the solution has a yellow colour |
| Bromothymol blue: Adding basic solution | Equilibrium is shifted to the right to oppose the increase in the concentration of OH⁻ BB⁻ becomes greater in concentration than HBB⁻ and the solution has a blue colour |
| Bromothymol blue: What is the transition point? | The mid-way point between the concentration of Hydronium and Hydroxide |
| Methyl orange | Methyl orange is a synthetic indicator often used in the analysis of weak bases The indicator changes colour between pH 3.1 and pH 4.4. Between these pH values, the indicator appears orange |
| Methyl orange : Colour Range | The indicator changes colour between pH 3.1 and pH 4.4. Between these pH values, the indicator appears orange Methyl orange is a weak acid |
| Phenolphthalein | Phenolphthalein is a synthetic indicator used in the analysis of weak acids. |
| Phenolphthalein: Colour Range | In acidic solutions, phenolphthalein is colourless, whereas in basic solutions it has a pink colour Chages colour over the pH range 8.3-10.0 Phenolphthalein is a weak base |
| Indicator range | The rang of pH values which an indicator changes colour |
| Why are indicators useful? | Indicators are useful in determining the equivalence point of a neutralisation reaction between an acid and a base. |
| What is meant by equivalence point? | The equivalence point in a titration at which exactly stoichiometric proportions have been added to achieve neutralisation |
| Volumetric analysis | Volumetric analysis is a quantitative technique in which volume of solutions of known concentrations are added to volume of solutions of unknown concentration/ |
| Titration | A titration is a form of analysis in which a base of known concentration and volume is reacted with an acid of unknown concentration. |
| End point | Point where the indicator changes colour Comes after the equivalence point Weak acids can only have one endpoint |
| What's the difference between end point and equivalence point? | The end point is the point in the titration at which the indicator changes colour. The equivalence point is the point in the reaction at which equivalent amount of acid and base have been mixed according to the ratio given in the chemical equation. |
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