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Rates of Reaction
| Question | Answer |
|---|---|
| What is the rate of a reaction | The change in concentration per unit of time of any reactant or product |
| Formula for the rate of a reaction | Rate = change in concentration/time |
| What is the instantaneous rate of a reaction | The rate of a reaction at any one particular time during the reaction. |
| All factors that affect the rate of a chemical reaction. (6) | 1. Nature of reactants 2. Pressure 3. Concentration 4. Temperature 5. Surface Area 6. Catalyst |
| How do the nature of reactants affect a chemical reaction. | At room temperature reactions that don't involve the breaking of bonds are fast as they require a small activation energy. For reactions that do require the breaking of bonds results in slower reactions as they need a larger activation energy |
| What is an effective collision | It is one that results in the formation of products. |
| What is activation energy | The minimum amount of energy required in colliding particles for a reaction to occur |
| What is the name of the graph that shows how a reaction occurred | Reaction profile diagram |
| What is a reaction profile diagram | A graph that shows the change in energy of a chemical reaction with time as the reaction progresses |
| List all the elements of a reaction profile diagram (4) | Reactants, activation energy, products, change in heat |
| What reaction gives out heat | Exothermic |
| What reaction takes in heat | Endothermic |
| How does temperature affect a chemical reaction. | Increase in effective collisions occurs. When the temp increases the particles are supplied with more energy causing them to move more sporadically. This results in more effective collisions as more particles are colliding at the activation energy needed |
| How does the surface area affect the rate of a reaction | The larger the area is the quicker the reaction occurs due to more active sites. The smaller the area the slower the reaction as there are less active sites. |
| What is a catalyst | A substance that alters the rate of a chemical reaction but is not consumed in the reaction. |
| How does a catalyst affect the rate of a reaction | A catalyst works by providing an alternate reaction pathway with a lower activation energy. |
| What is an enzyme | A substance that is produced in living cells and acts as a biological catalyst. |
| What are the properties of a catalyst 1-3 | 1. Catalysts are recovered at the end of an experiment chemically unchanged. 2. Catalysts are specific meaning they catalyse a certain class of very similar reactions. 3. Catalysts only need to be in small amounts to function as catalysts. |
| What are the properties of a catalyst 4-5 | 4. In equilibrium reactions, a catalyst helps equilibrium be achieved more quickly. 5. The action of a catalyst may be destroyed by certain substance called catalytic poisons. |
| What is an example of a catalytic poison | Lead in catalytic converters in cars |
| What are the three types of catalysis | 1. Homogenous catalysis 2. Heterogeneous catalysis 3. Autocatalysis |
| What is homogenous catalysis | Catalysis where the reactant and catalyst are in the same phase with no boundary |
| Example of homogenous catalysis | Potassium Iodide + hydrogen peroxide |
| What is heterogeneous catalysis | Catalysis where the reactant and catalyst are in different phases. There is a boundary between the two |
| Example of heterogeneous catalysis | Manganese dioxide + hydrogen peroxide |
| What is autocatalysis | When the product of the reaction is used as a catalyst for the reaction |
| Example of autocatalysis | Potassium permanganate + Oxalic acid |
| Explain the intermediate formation theory | W+X -> Y+Z W+C -> [WC] [WC] + X -> Y+Z+C |
| Example of the intermediate formation theory in effect | Potassium sodium tartrate + Hydrogen Peroxide + Cobalt (II) Chloride |
| What colour change is evident in the intermediate formation theory experiment | Pink -> Green -> Pink |
| What are the three stages involved in the surface adsorption theory. | 1. Adsorption Stage 2. Reaction on surface 3. Desorption Theory |
| What happens during the first stage of the adsorption theory | Hydrogen and oxygen molecules diffuse and absorb onto the surface of the platinum. The oxygen and hydrogen are held onto the surface by temporary bonds formed by the platinum. The platinums vacant d orbital help this to happen. |
| What happens during the second stage of the absorption theory | Due to adsorption the higher concentration of molecules on the surface makes it more likely that these molecules will collide with each other. Old bonds are broken and new ones are formed. Water moles are formed on the platinum. |
| What happens during the final stage of the adsorption theory | The water molecules leave the surface of the catalyst and diffuse away from the catalyst. More reactants adsorb on the surface and the process repeats |
| A reaction that has more products than energy is called | An endothermic reaction |
| A reaction that has less products than energy is called | An exothermic reaction |
| How does concentration affect the rate of a reaction | The greater the concentration the more particles there are causing an increase in effective collisions. The smaller the concentration the less particles there are. |
| What are the limitations on the rate of a reaction (sat.) | If catalysts become saturated all the sites will be occupied. Since there still are reactants the effectiveness of the catalyst will reduce. |
| What are the limitations on the rate of a reaction (cp) | Catalytic poisons can destroy the effectiveness of a catalyst. These poisons form a permanent bond with the catalyst |
| What are the limitations on the rate of a reaction (or.) | In order for a collision to be successful, particles must be orientated correctly |
| What reactions does pressure only affect | Gaseous reactions |
| How does pressure affect the rate of a reaction |
Created by:
Miki_Szn
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