Topic 7 - Rates of Reaction and Energy Changes
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What is the rate of a reaction?
How quickly a reaction happens
How can you observe the rate of reaction?
How quickly reactants are used up How quickly products are formed
What is the rate of reaction equation?
Rate of Reaction = (Amount of reactant used or amount of product formed) / Time
What are the experiments to measure the rate of reaction?
Change in mass Precipitation Volume of gass given off
What is the precipitation experiment?
Using two see-through solutions to form a precipitate which clouds a mark
What is the problem with the precipitation experiment?
Subjective as different people might not agree on exactly when the mark disappears
How do you measure the rate of reaction that produces a gas?
By using a mass balance
When using change in mass to measure the rate of reaction, how do you tell the reaction is finished?
The mass balance stops changing
What risks are associated with measuring the volume of gas to calculate the rate of reaction?
The plunger may be blown out of the syringe if the reaction is too vigorous
Outline how you could use a mass balance to measure the rate of a reaction where a gas is formed?
Put a conical flask on a mass balance and add your reactants. As gas is produced from the reaction, measure how quickly the reading on the balance drops until the balance stops changing
Give one disadvantage of the precipitation method when used to follow the rate of a reaction?
No quantitive result (except time, no amount of reactant used or product formed) Subjective meaning different people might not agree on exactly when the mark ‘disappears’
How can you measure how surface area affects the rate of reaction?
Add marble chips to dilute HCL and measure the gas released Each time crunch the chips up more and more, increasing the surface area, whilst keeping the mass the same
What does finer particles of solid mean?
A higher rate of reaction
How can you increase the volume of gas produced in a reaction?
By increasing the mass of the reactants
How can you measure how concentration affects the rate of reaction?
Add marble chips to dilute HCL and measure the gas released Each time increasing the concentration of acid
Describe how you could investigate how the surface area of calcium carbonate affects the rate of reaction between calcium carbonate and hydrochloric acid?
Place a measured volume of HCL of a known conc in a conical flask Add a known mass of calcium carbonate in the form of marble chips Immediatly add a gas syringe and take readings of the volume of gas produced Repeat the experiment but with the calcium carbonate crushed
What reactants are used to investigate the effect of temperature on the rate of reaction?
Sodium thiosulfate Hydrochloric acid
What do sodium thiosulfate and hydrochloric acid react to form?
A yellow precipitate of sulfur
Briefly describe the method of investigating temperature and reaction rate
Measure out fixed volumes of sodium thiosulfate and hydrochloric acid Heat the reactants to a desired temperature and mix the solutions Time how long it takes for the precipitation to make the black mark disappear Repeat experiment at different temperatures
Briefly describe the method of investigating temperature and reaction rate
Measure out fixed volumes of sodium thiosulfate and hydrochloric acid Heat the reactants to a desired temperature and mix the solutions Time how long it takes for the precipitation to make the black mark disappear Repeat experiment at different temperatures
When measuring how surface area affects ROR, what are the control variables?
The same volume and concentration of acid The same mass of marble chips
When measuring how concentration affects ROR, what are the control variables?
The same mass and surface area of marble chips The same volume of hydrochloric acid
What does a higher temperature mean?
A higher rate of reaction
Azim carries out an experiment to measure how temperature affects the rate of reaction between sodium thiosulfate and hydrochloric acid He uses the time taken for a mark underneath the reaction vessel to be obscured as a measure of rate How would you expect the time taken for the mark to disappear to change as the temperature of the reacting solutions were increases?
As the temperature of the reacting solutions increases, the time taken for the mark to disappear decreases