7.1 Rates of Reaction
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Rate of reaction
How quickly a reaction happens
Rate of reaction formula
Rate of reaction = amount of reactant used up or product formed/time
Names of the methods to measure reaction rates
-Precipitation -Change in mass -Volume of gas
Experiment to measure the rate of reaction with precipitation
1- Mix the two reactant solutions and put the flask on a piece of paper that has a mark on it 2- Observe the mark through the mixture and measure how long it takes for the mark to be obscured
Problem with the precipitation method for reaction rates
People might not agree on exactly when the mark disappears
When should you use the precipitation experiment for measuring the rate of a reaction
When two see-through solutions produce a precipitate which clouds the solution
When should you use the change in mass method for measuring the rate of a reaction
When a gas is a product of a reaction
Experiment to measure the rate of a reaction with the change in mass
1- Start the reaction in an open conical flask with cotton wool in on a mass balance. 2- As the gas is released the new mass is shown on the balance. After chosen time intervals, record the mass on the balance 3- Once the mass stops changing plot your results on a graph of change in mass against time
Problem with the change in mass rate of reaction experiment
-The gas is released straight into the room- which is bad if it is harmful -If the flask is too hot, some liquid may be lost due to evaporation
Why is the conical flask blocked with cotton wool in the rate of reaction experiment using change in mass
As gases can pass through, but solid, liquid or aqueous reactants can’t fly out
When should you use the volume of gas method for measuring the rate of reaction
When a gas is released as a product
Experiment to measure the rate of reaction using the volume of gas
1- Connect a conical flask with a bung to a gas syringe with a delivery tube 2- Start the reaction and a timer and measure the volume in the gas syringe after specific intervals 3- When no more gas is produced, plot a graph of gas volume against time
Problem with the volume of a gas method for measuring the rate of reaction
If you are not using the right size gas syringe and the reaction is too vigorous, it could blow the plunger off the end of the syringe
Experiment to measure how surface area affects rate using marble chips and acid
1- Measure out and record a mass of marble chips and a volume of acid 2- Conduct the volume of a gas reaction rate experiment 3- Repeat the experiment with the same mass of marble chips and volume of acid but the marble chips are grinded
Finer particle
A particle with a larger surface area
How will using finer particles affect the rate of reaction
The finer the particles, the faster the reaction
How does the concentration of reactants affect the rate of reaction
The higher the concentration the faster the reaction
Experiment to investigate the effect of concentration on rate of reaction
1- Measure and record a volume of acid and mass of marble chips 2- Conduct the change in mass experiment for rate of reaction 3- Repeat using the same mass of marble chips and volume of acid but change the concentration of acid
Experiment to investigate the effect of temperature on rate of reaction
1- Measure out fixed volumes of two colourless solutions 2- Use a water bath to gently heat both solutions to a desired temperature 3- Conduct the precipitation method for rate of reaction 4- Repeat this at different temperatures with solutions of the same volume, depth and concentration
What should the graph for how temperature affects rate of reaction look like (precipitation method)
Time for X to be obscured against temperature
How does temperature affect rate of reaction
Higher temperature means faster rate of reaction
Collision theory
The theory behind how particle collisions cause reactions
What does the rate of a reaction depend on (collision theory-wise)
-The collision frequency of reacting particles -The energy transfered during a collision
How does the rate of successful collisions affect rate of reaction
The more successful collisions, the faster the reaction