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Rates of Reaction
Rates of Reaction Chapter 16
| Question | Answer |
|---|---|
| Define the rate of reaction | Rate of reaction: Change in concentration per unit time of any one reactant or product Change in amount of reactant or product over change in time |
| What is the average rate of reaction? | Average reaction rate is the rate of change over a period in time. total change in reactant or product over total time |
| What is the instantaneous rate of reaction? | The instantaneous rate is the rate of reaction at one particular time during the reaction |
| How would you calculate the instantaneous rate of reaction | Write down the slope of the line formula y1 - y2 ________ x1 - x2 Draw a tangent to the curve at the specific minute mark on the graph |
| How do you calculate the initial rate of reaction? | Draw a tangent lina from the t=0. Use the slope formula |
| What is collision theory? | Collision theory states that the particles must collide with one another to react. The particles must have sufficient energy to have an effective collision |
| What is an effective collision | One that results in the formation of products |
| Define activation energy | Minimum energy that colliding particles must have for an effective collision to occur |
| List the five factors that affect the rate of reaction | Temperature Surface area concentration Catalyst Pressure (For all gaseous reactions) |
| Describe how temperature affects the rate of a reaction | Increased temperature increases the rate of reaction, therefore decreases the reaction time. Particles have increased kinetic energy which means the particles reach the activation energy quicker. Therefore there are more effectivecollisonsperunitpertime |
| Describe how concentration affects the rate of a reaction | Greater concentration of reactants, then the faster the reaction will be. The more particles the greater the chance of there being an effective collision per unit time. |
| What is a catalyst? | A substance that alters the rate of reaction but is not used up in the reaction. |
| What is an enzyme? | It is a biological catalyst |
| How do catalysts work? | Catalysts increase the rate of reaction by: Providing an alternative pathway with a lower activation energy |
| Describe how surface area affects the rate of a reaction | The smaller the particle size, the more surface area and therefore greater number of effective collisions per unit time. |
| Describe how the nature of reactants affects the rate of reaction | The rate of a reaction will depend on the bonds involved Ionic bonds are generally fast as there is no bond breaking or forming. Covalent bonds are generally slower as bonds need to be broken before a reaction could take place. |
| Describe how the pressure affects the rate of reaction | For reactions happening between gases, increasing the pressure reduces the volume. This increases the number of reacting particles per unit volume and therefore the number of effective collisions per unit time. |
| What are the properties of a catalysts | Catalysts are specific Only needed in small amounts Can be inhibited/destroyed by a catalytic poison Catalysts are often transition metals. In the case of an equilibrium reaction, a catalyst helps equilibrium be achieved more quickly. |
| What are the steps in the Surface Adsorption Theory | 1. Adsorption 2. Reaction on the surface 3. Desorption |
| Explain the first step of the Surface Adsorption Theory: Adsorption | Reactants adsorbed onto the surface of the catalyst in the correct orientation and in high concentration. Temporary weak bonds form between the reactant and the catalyst |
| Explain the second step of the Surface Adsorption Theory: Reaction on the surface | There is a high concentration of reactants Effective collisions occur causing a reaction to happen. Products are formed |
| Explain the third step of the Surface Adsorption Theory: Desorption | The products leave the surface of the catalyst |
| What is a Heterogeneous Catalysis | The reactant(s) and catalyst are in different phases |
| What is the Intermediate formation theory | W + X -------->Y + Z A catalyst © forms an intermediate with a reactant. [WC] + X--------->Y+Z +C The intermediate reacts with the other reactant to form products. Products are formed and the catalyst is released. |
| What happens in the Intermediate formation theory of catalysis, Oxidation of potassium sodium tartrate by hydrogen peroxide & catalysed by cobalt(II) | Pink at the beginning of the reaction colour of the catalyst Co2+ solution Bubbling and gas are produced as reaction mixture turns green due to formation of intermediate complex Pink at the end as the reaction finished and the catalyst Co2+ is regend |
| What is a homogenous Catalysis | The reactant(s) and catalyst are in the same phase i.e. the same boundary i.e. iodine snake |
| What is autocatalysis | One of the products of the reaction acts as catalyst for the reaction. |
| What are the 3 parts of the Limitations of the collision theory | 1. Orientation 2. Catalysts 3. Concentration |
| Explain the 1st part of the Limitations of the collision theory: Orientation | Particles must collide in the correct orientation for a reaction to occur but it makes it less accurate at predicting rates of reactions involving complex molecules. |
| Explain the 2nd part of the Limitations of the collision theory: Catalysts | Saturation of catalysts If the surface of the catalyst is fully occupied by the reactant molecules, increasing the concentration will have no effect on the rate of reaction |
| Explain the 2nd part of the Limitations of the collision theory: Catalysts | Poisoned catalysts A catalyst poisons can permanently adsorb onto its surface. It causes the catalyst to stop working |
| Explain the 3rd part of the Limitations of the collision theory: Concentration | Limiting reagents: When a reaction involves multiple reactants, an increase in the concentration of one reactant may not alter the rate of reaction unless there is a sufficient amount of the other reactants also present. |
| Explain the 3rd part of the Limitations of the collision theory: Concentration | A reaction with numerous steps: Some complex reactions happen in several steps. The slowest step in a reaction mechanism is the one that controls the overall rate at which the reaction proceeds and is called the rate determining step. |
| Explain the 3rd part of the Limitations of the collision theory: Concentration | It usually has the highest activation energy. An increase in concentration may not change the overall speed of the reaction if it doesn't alter the rate determining step. |
| What is a reaction profile diagram? | Graph that shows the change in energy of a chemical reaction with time as the reaction progresses. |
| What is an Exothermic Reaction? | a chemical reaction that releases energy into its surroundings, typically as heat, causing the temperature of the surroundings to increase |
| What is an Endothermic Reaction? | a chemical process that absorbs energy, usually heat, from its surroundings, causing the surroundings to become colder. |
| What effect does a catalyst have on activation energy | It makes the activation energy smaller |
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21JulianM
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