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CC14H SC18H

Pearson GCSE Combined and Separate Chemistry Higher

QuestionAnswer
Define the rate of a reaction. The rate at which reactants are used up or products are made.
Describe or sketch a reactants vs time graph Starts high and curves downward, decreasing rapidly at first and then more gently.
Describe or sketch a products vs time graph Starts low and curves upwards, increasing rapidly at first and then more gently.
Explain two of the three ways the rate of a reaction that produces a gas can be measured. Collect gas in a gas syringe and measure the volume every 30 secs/ Collect gas over water (up-turned measuring cylinder full of water) and measure volume every 30 secs/ Do reaction on a balance and record the change in mass every 30 secs.
Explain how the rate of a reaction that goes cloudy can be measured. Do the reaction in a beaker placed on piece of paper with a cross marked on it. Looking down through the beaker, time how it takes for the cross to disappear.
What are the two statements of the collision theory of reactions? States that for two particles to react they must: Collide with each other / Collide with enough energy to react
Define the activation energy of a chemical reaction. The minimum energy that two particles must have when they collide in order to react.
Explain the effect of increasing the concentration on the rate of a reaction in terms of collision theory Increasing the concentration increases the rate because there are more particles so there are more collisions and more reactions.
Explain the effect of increasing the surface area on the rate of a reaction in terms of collision theory Increasing the surface area (by decreasing particle sizes) increases the rate by exposing more particles to collisions leading to more collisions and more reactions.
Explain the effect of increasing the pressure on the rate of a reaction in terms of collision theory Increasing the pressure increases the rate because particles are pushed closer together so they collide more often
Explain the effect of increasing the temperature on the rate of a reaction in terms of collision theory Increasing the temperature increases the rate because particles move faster so they collide more, and collide with more energy to a greater proportion of collisions lead to reactions.
What is a catalyst? A substance that speeds up a chemical reaction without being used up.
Explain the effect of a catalyst on the rate of the reaction. Catalysts increase the rate of reaction by reducing the activation energy so that a greater proportion of collisions lead to reactions.
What is the rate of a chemical reaction in terms of reactants? How quickly the reactants in a reaction are used up
What is the rate of a chemical reaction in terms of products? How quickly the products in a reaction are formed
What is the formula for a mean rate of reaction in terms of reactants? quantity of reactant used/time taken
What is the formula for a mean rate of reaction in terms of products? quantity of reactant product formed/time taken
How can you measure the quantity of a reactant or product? In grams or in cm³
What are the two possible units for rate of reaction? g/s or cm³/s (where s is seconds)
How could you measure the rate of a reaction from a graph? Draw a tangent to the curve and calculate the gradient.
What is "collision theory"? The theory that chemical reactions only occur when particles collide with sufficient energy
What factors can affect the rate of a reaction? Temperature, surface area of a solid, concentration or reactants in solution, pressure of gases
State the effect of increasing the surface area on the rate of a reaction Increases the rate
Explain why increasing the surface area increases the rate of a reaction More particles are available to collide, there are therefore more frequent collisions between reactants.
State the effect of increasing the concentration on the rate of reaction Increases
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
What supplies the enzyme for producing alcoholic drinks Yeast
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