SC18 Rates of Reaction
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Define rate of reaction
The speed at which reactants are turned into products
How can we control the rate of a reaction?
By controlling the variables
What are three commonly used techniques to measure the rate of a reaction?
• measuring mass lost on a balance • measuring the volume of a gas produced • measuring a reaction where there is a colour change at the end of the reaction
How can we use the change in mass to find the rate of the reaction?
• when gas is produced in a reaction, it usually escapes the reaction vessel, causing a loss in mass • the difference between the initial mass and the final mass can be used to find out the rate of the reaction • in a set period of time
When are reaction rates usually the fastest and why?
At the start, because that is when the concentrations of all the reactants are the greatest
When is measuring the change in mass not suitable?
When the gases produced have a small relative formula mass
How can the rate be calculated?
(reactant used or product formed)/time taken
When do we measure the change in the volume of a reactant or a product?
When a gas leaves the container
How do we measure the volume of the gas leaving the reaction container?
Using: - a gas syringe - upside down burette - measuring cylinder
What is the collision theory?
When reactants come together, the kinetic energy they possess means that their particles will collide and some of these collisions will result in chemical bonds being broken and new bonds being formed
What must occur for a chemical reaction to take place?
• particles must collide with each other • particles must have enough energy for them to react
Define activation energy
The minimum amount of energy needed for a collision to be successful
What is the effect of increasing the concentration or pressure of a reacting component?
• the reactant particles are closer together • the frequency of collisions between the reactant particles increases • therefore increasing the rate of reaction
What factors affect the rate of reaction?
• concentration and reaction rate • surface area • pressure of gases • temperature
How does the concentration of solutions increase the rate of reaction?
There are more reacting particles in the same volume so collisions occur more often
How does an increase in surface area increase the rate of reaction?
More surface area of the particles will be exposed to the other reactant, producing a higher number of collisions per second
How does an increase in the pressure increase the rate of reaction?
Reactant particles are squeezed closer together so collisions occur more often
How does an increase in temperature result in an increase in the rate of reaction?
Particles will have more kinetic energy than the required activation energy , therefore there will be more frequent and successful collisions per second
What variable is usually plotted on the x axis of a rate graph?
Time
What are catalysts?
A substance that increases the rate of a reaction without altering the products of the reaction. It is chemically unchanged by the end of the reaction
What do catalysts do?
Provide an alternative route for the reaction to take place
What is the effect of a catalyst on the activation energy?
Lowers the activation energy, which provides a pathway requiring less energy
Define enzymes
Biological enzymes
Name an example of a enzyme
Yeast enzymes