Chapter 8 Rates of Reaction Flashcards
(32 cards)
What does “rate of reaction” refer to?
The speed at which a reaction takes place. It is usually expressed as a change over time for example: volume of gas produced (cm3) / second, change in mass (g)/second.
Give 2 ways the rate of reaction can be determined.
Monitoring the reduction in reactants over time.
Monitoring the production of products over time.
What formula can you use to calculate the mean rate of reaction?
Describe how the rate of reaction could be determined using loss in mass if a gas is produced in the reaction.
In a reaction where one of the products is a gas then the reactants can be placed in an open flask on a scale. Cotton wool in the opening allows gas to escape but retains other contents. The mass will decrease as the reaction progresses.
Draw and label a graph to show what happens in a loss of mass experiment.
Draw a diagram to show the equipment needed to measure the volume of gas collected over time during a reaction.
Draw and label a graph to show what happens in a production of gas experiment.
How can you tell the time when the rate of reaction is fastest by looking at a graph?
(HIGHER ONLY)
Draw a tangent. The greatest rate of reaction is where the tangent is steepest.
How can you calculate the rate of reaction at a specific time?
(HIGHER ONLY)
Calculate the gradient of the tangent at that time.
Describe how to calculate the rate of reaction when an insoluble precipitate is produced.
When an insoluble precipitate is produced the reaction mixture turns cloudy. If a flask is placed on an X we can time how long it takes for the X to no longer be visible.
How does decreasing the particle size of a solid reactant affect the rate of reaction?
Decreasing the particle size increases the rate of reaction.
Why does decreasing the particle size increase the rate of reaction?
Smaller particles have a larger surface area. This increases the number of collisions between reactants and speeds up the rate of reaction.
How does increasing the temperature affect the rate of reaction?
Increasing the temperature increases the rate of reaction.
Why does increasing the temperature increase the rate of reaction?
At higher temperatures:
1. The particles collide with more energy so are more likely to react.
- There are more collisions.
What correlation is there between time and the production of gas?
Positive correlation - a tangent drawn to calculate the initial rate of reaction is a straight line that goes up.
What correlation is there between time and loss of mass?
Negative correlation - a tangent drawn to calculate the initial rate of reaction is a straight line that goes down.
How does increasing the concentration of reactants affect the rate of reaction and why?
As the concentration of reactants increases the rate of reaction increases because the particles are closer together in concentrated solution and gases as the frequency of collisions increases.
How does increasing the pressure affect the rate of reaction and why?
Increasing the pressure of a gas causes the particles to get closer together. This increases the frequency of collisions and therefore the rate of reaction.
What is a catalyst?
A catalyst is a substance that increases the rate of a chemical reaction without being used up.
What is an enzyme?
An enzyme is a biological catalyst.
How do catalysts speed up chemical reactions?
Catalysts speed up chemical reactions by lowering the activation energy needed for reactants to react. This increases the frequency of successful collisions.
What symbol is used to represent a reversible reaction?
Describe the energy changes that take place in a reversible reaction.
In one direction the reaction is exothermic and in the other direction the reaction is exothermic. The energy required for the reaction in one direction is the same as the energy released in the other direction.
What units do we use to measure energy in chemical reactions?
Kilojoules (kJ).
