(b) Controlling the rate Flashcards
What is the rate of reaction?
The speed at which the reaction occurs.
What must happen for a reaction to occur?
Reactant particles must collide with sufficient kinetic energy, it must be greater than the activation energy.
And have the correct collision geometry.
What is the formula to work out average rate of reaction?
Change in quantity/ change in time.
What are the 2 ways to collect and measure gas?
Use a gas syringe and downwards displacement through water.
What is a way which you can measure the course of a reaction?
Measuring the change in mass.
What are the 4 factors affecting rate of reaction?
Temperature
Concentration
Particle size
Use of a catalyst.
What is the activation energy?
The minimum energy required by colliding particles to produce an activated complex.
What does increasing the concentration do to the rate of reaction?
Increases it.
Why does increasing the concentration increase the rate of reaction?
There are more particles in the same space, this means more collisions are likely. When particles collide with sufficient energy a reaction will occur.
How does particle size affect the rate of reaction?
A bigger particle size means that there is less surface area and so less collisions occur. A smaller particle size increases the amount of surfaces and so more collisions occur.
What is an activated complex?
An activated complex is an unstable arrangement of atoms formed at the maximum of the potential energy barrier during a reaction.
In an exothermic reaction what happens?
Energy, in the form of heat, is given out.
What is the energy relationship between the products and reactants in an exothermic reaction?
The products have less energy than the reactants.
What is the delta H always in an exothermic reaction?
Negative.
Describe a potential energy diagram for an exothermic reaction.
It will go along, up and then down and along, and the second line will be lower than the first.
What is an exothermic reaction?
One in which energy is absorbed from the surroundings.
What is the delta H always in an exothermic reaction?
Positive.
Describe the potential energy diagram of an endothermic reaction.
It will go along, up, down, and along. The second line will be higher up than the first.
What does a distribution curve show?
The amount of reactions that result in a reaction, OR the amount of collisions that collide with the sufficient activation energy.
What is a catalyst?
A catalyst provides an alternative route which involves less energy and so lowers the activation energy.
What is a homogeneous catalyst?
A catalyst which is in the same state as the reactants.
What is a heterogeneous catalyst?
A catalyst which is in a different physical state to the reactants.
Does a catalyst affect the delta H value?
No.
What are the 3 stages in a reaction with a catalyst?
Adsorption, Reaction, Desorption.
What is the delta H value?
The difference in energy between the reactants and the products.
How does pressure affect the rate of reaction?
The higher the pressure, the less space there is and so the likelihood of collisions is increased and so the reaction rate is increased.
How does temperature affect the rate of reaction?
An increase in temperature increases the genetic energy of the reactants, meaning they move faster, this means that they are more likely to collide thus increasing the rate of reaction.
How much do you need to increase the temperature to see a large increase in the rate of reaction?
If you increase by only 10 degrees it will almost double the rate.
What is temperature a measure of?
Temperature is a measure of the average kinetic energy of the particles in a substance.
