Unit 3-Controlling the Rate Flashcards
Why is it important to be able to control reaction rates?
To ensure that processes are
- economically viable (they will result in a good yield of products and profits for the company)
- safe (the reaction does not progress too quickly potentially causing explosions).
How can average rate and reaction rate be calculated?
Average rate = ΔQuantity/Δtime
Reaction rate = 1/t
What is meant by Collision Theory?
Collision theory can be stated as:
particles must collide to react
but not all collisions are successful.
There must be
- sufficient energy
- Orientation must be correct.
Explain why for a chemical reaction to occur, the reactant molecules must collide with enough energy.
They must have enough energy to overcome the repulsive forces (caused by outer electrons) and start to break the bonds between the atoms.
What is the name given to a high-energy intermediate state that is established when bonds inside the reactant molecules are breaking and new bonds are being formed?
Activated complex
Use collision theory to explain the effects of the collision geometry on reaction rates.
For a successful collision to take place, the collision geometry must be right (the reactant molecules have to be facing the right way!) so that the activated complex can be formed.
Which of the following collisions is most likely to result in a successful reaction?
A
Use collision theory to explain the effects of the temperature on reaction rates.
If the temperature is increased, the particles have more kinetic energy and so move more quickly.
Increasing the temperature increases the rate of reaction because the particles collide more often.
Higher chance of successful collisions
Use collision theory to explain the effects of concentration on reaction rates.
If the concentration of reactants is increased, there are more reactant particles moving together. There will be more collisions, a higher chance of successful collisions and so the reaction rate is increased. The higher the concentration of reactants, the faster the rate of a reaction will be.
Use collision theory to explain the effects of the particle size on reaction rates.
By decreasing the particle size of a reactant, we are increasing its surface area.
A smaller particle size of reactants provides a greater surface area that collisions can take place on.
The greater the surface area, the faster the rate of reaction.
Higher chance of successful collisions
What is meant by activation energy?
Minimum energy required for a reaction to occur
If a reaction has a low activation energy then will the reaction be fast or slow?
Fast as a lot of particles will have the required energy.
ΔH is the overall enthalpy change for a reaction.
Will an exothermic reaction have a positive or negative enthalpy change?
An exothermic reaction is one in which heat energy is given out. The products must have less energy than the reactants because energy has been released.
For exothermic reactions, ΔH will always be negative
ΔH is the overall enthalpy change for a reaction.
Will an endothermic reaction have a positive or negative enthalpy change?
An endothermic reaction is one in which heat energy is absorbed. The products must have more energy than the reactants because energy has been taken in.
For endothermic reactions, ΔH will always be positive.
