AQA GCSE Chemistry 4.6 - Rate and Extent of Chemical Change

AQA GCSE Chemistry 4.6 - Rate and Extent of Chemical Change 1. How is the rate of a chemical reaction measured in terms of reactants? Answer: The rate of a chemical reaction can be measured by tracking how quickly the reactants are used up. 2. What is the relationship between the rate of a chemical reaction and products? Answer: The rate of a chemical reaction is also reflected in how quickly the products are formed. 3. What is the formula for calculating the mean rate of reaction in terms of reactants? Answer: The formula is quantity of reactant used per unit time, typically expressed in units such as grams per second (g/s) or cubic centimeters per second (cm³/s). 4. How can you calculate the mean rate of reaction in terms of products? Answer: The formula is quantity of product formed per unit time, also expressed in units such as g/s or cm³/s. 5. What are common units for measuring the quantity of reactants or products? Answer: The most common units are grams (g) or cubic centimeters (cm³). 6. What are the two possible units for expressing the rate of reaction? Answer: The two possible units are grams per second (g/s) and cubic centimeters per second (cm³/s). 7. How can you determine the rate of reaction from a graph? Answer: By drawing a tangent to the curve and calculating its gradient, which represents the rate at which reactants are converted to products. 8. What is collision theory, and how does it relate to chemical reactions? Answer: Collision theory proposes that chemical reactions occur only when particles collide with sufficient energy, allowing them to overcome activation energy barriers. 9. What factors can influence the rate of a chemical reaction? Answer: Factors that can affect the rate of a reaction include temperature, surface area of solid reactants, concentration of reactants in solution, and pressure of gases. 10. What effect does increasing the surface area have on the rate of reaction? Answer: Increasing the surface area typically increases the rate of reaction, as more particles are available to collide and react. 11. Why does increasing the surface area increase the rate of reaction? Answer: With more particles available, there are more frequent collisions between reactants, leading to a faster rate of reaction. 12. What effect does increasing concentration have on the rate of reaction? Answer: Increasing concentration typically increases the rate of reaction, as there are more particles available for collisions. Explain why increasing the concentration increases the rate of reaction More concentrated means more particles in solution, therefore more frequent collisions between reactants. State the effect on increasing the pressure of a gas on the rate of reaction Increases Explain why increasing the pressure of a gas increases the rate of a reaction Less space for the particles to move around in, therefore more frequent collisions State the effect of increasing the temperature on the rate of reaction Increases What is the activation energy? The amount of energy a particle needs before it will be able to react when it collides with another particle Explain why increasing the temperature increases the rate of reaction Increases the speed at which particles move therefore more frequent collisions. Increases the number of particles which have the activation energy therefore more collisions result in a reaction. What is a catalyst? Something which changes the rate of a reaction but is not used up in that reaction How do catalysts speed up reactions? They provide another route for the reaction to take place which has a lower activation energy. Draw a reaction profile for an exothermic reaction and show the effect of adding a catalyst. reaction rate How quickly a reaction takes place. Measured by the change in amount of reactant or product divided by the time taken. excess Any reagent that has had enough added so that there is still some left after the reaction has ended. This ensures that all o the other reagent will be used up. limiting reagent A reagent not in excess that determines the final amount of product that will be produced. temperature A measure of the average kinetic energy of the particles in a substance. Increasing this will increase the rate of reaction. concentration A measure of the amount of solute dissolved in a solvent. Increasing this will increase the rate of reaction. pressure A measure of the force exerted by gas particles colliding with the walls of a container. Increasing this will increase the rate of reaction.