The rate of reaction is measured by investigating how much reactant is used up or how much product is formed in a certain time.
? TEST TUBE
1. Research the rates of the following reactions and place them in order, from fastest to slowest: • wine fermenting • baking a cake • dynamite exploding • milk going sour
• limestone rock weathering • an iron nail rusting
• an antacid tablet relieving symptoms of heartburn
Rate of reaction graphs The slope of a graph can be used to show the rate of a reaction.
• A fast reaction produces a lot of product quickly. This results in a steeper slope on the curve when plotted on a line graph.
• As the reactants are used up, no more product is formed. This results in the line levelling off on the line graph.
Reaction finishes as the reactants get used up
Reaction slowing
Fast reaction
The steeper the graph, the quicker the reaction takes place
Slow reaction
) Fig. 21.3 A rate of reaction graph
Time ? TEST TUBE
2. Students investigated the reaction between magnesium and hydrochloric acid, which produces magnesium chloride and hydrogen gas. Their results are shown in the table below:
Investigation Time needed to collect 10 cm3 of hydrogen gas (s) AB C
a. Which investigation had the slowest rate of reaction? b. Which investigation had the fastest rate of reaction? c. In which investigations is it likely that the testing conditions were the same?
d. The only variable the students changed was the temperature. Which investigation took place at the highest temperature? Explain your answer.