Rates of Reaction Flashcards
What would the rate of any reaction depend on in relation to collision theory?
The rate of any reaction would then depend on the number of effective collisions occurring per
second between reacting molecules. This is known as the collision theory.
Define reaction rate.
Reaction rate is the change in concentration per unit time of either a reactant or product.
True or false
The formulae express an average rate because the rate of any reaction is not constant as the reaction proceeds.
True
What is the gradient a measure of?
The gradient is a measure of the reaction rate. The gradient is also greatest at the start of a reaction.
The gradient of the tangent to the curve is the _____ reaction rate while the gradient of the line joining two points on the graph is the a ____ reaction rate over that interval.
Instantaneous
Average
What can the amount of reactant and product be measured in?
The amount of reactant and product can
be measured in units of moles, grams or volume depending on the
experiment.
How can the rate of a reaction be measured?
The rate of a reaction can be measured by determining the amount of reactant used per time or the amount of product produced per time.
What the methods of measuring rates of reaction? (4)
- Change in colour
- Turbidity (eg. Precipitate formation)
- Change in mass
- Change in volume of a gas produced
Why is measuring the change in volume of a gas produced a suitable method of measuring the rate of a reaction?
This is a suitable method if one of the products is a gas. We can collect the gas in a gas syringe and measure the amount of gas collected at various times.
How is measuring the change in mass a suitable method for measuring rates of reaction?
Many reactions involve a change in mass which can be measured directly.
The reaction mixture is placed directly on a mass scale and either the total mass or the mass loss is recorded at convenient time intervals. The reaction vessel cannot be sealed for this method to work.
How is turbidity a suitable method for measuring the rate of a reaction?
In reactions where a precipitate is formed, the amount of precipitate formed in a period of time can be used as a measure of the reaction rate.
Why is measuring the change in colour a suitable method of measuring the rate of a reaction?
In some reactions, there is a change in colour that allows us to determine when a particular point in the reaction has been reached. For example, an indicator changes colour depending on the acidity of the solution.
The rate of reaction is determined by the nature of the reactants and the conditions of the reaction.
What are the factors affecting rate of reaction? (5)
Factors affecting rate of reaction From our practical investigations, we have determined that the factors that affect the reaction rate are: • surface area (solid) • concentration (solution) • pressure (gas) • temperature • catalyst
How does surface area affect the rate of a reaction?
Increasing the surface area of a solid increases the rate of reaction. Crushing a sample of solid into smaller pieces means that the surface are is larger which means that more of the solid is exposed. This allows for more contact and a greater chance of effective collisions.
Eg. When lighting a fire, small pieces of wood rather than a log is used. Explosions can occur in flourmills due to the tiny particle sizes.
How does concentration of the reactants affect the rate of a reaction?
Increasing the concentration of the reactants increases the rate of reaction. Increasing the concentration means that there are more reactants per unit volume of solution which allows for more collisions between reactants. More collisions in turn mean that there will be more effective collisions and greater rate of reaction.
This also explains why the rate of reaction decreases over time in a reaction. As reactants are used up, the concentration decreases and hence the rate of reaction decreases.
