Section 7 - Rates of reaction and energy changes - Rate of reaction

Question 1

What is rate of reaction?

Answer 1

Measure of how fast the reaction happens

Question 2

Formula for rate of reaction?

Answer 2

Rate of reaction = ‘amount of reactant used’ or ‘amount of product formed’ ÷ time

Question 3

3 ways how rate of reaction is measured?

Answer 3

Precipitation, change in mass (usually gas given off), volume of gas given off

Question 4

Method for measuring ‘precipitation’ for rate of reaction?

Answer 4

Mix 2 reactant solutions and put flask on paper with ‘X’ on it. Observe mark through mixture and measure time taken for mark to be obscured. Faster it disappears, faster reaction

Question 5

2 cons of measuring ‘precipitation’ method for rate of reaction?

Answer 5

Result is subjective - different people might not agree on exactly when mark disappears
Only works for reactants that produce precipitate

Question 6

Method for measuring ‘change in mass’ for rate of reaction?

Answer 6

As gas released, lost mass measured on balance. Quicker reading on balance drops, faster reaction. Reaction finished when reading on balance stops changing.

Question 7

Con of measuring ‘change in mass’ for rate of reaction?

Answer 7

Method does release gas produced into room so if harmful, must take safety precautions

Question 8

Method for measuring ‘volume of gas given off’ for rate of reaction?

Answer 8

Use gas syringe to measure volume of gas given off. More gas given off during time interval, faster reaction. Reaction finished when no more gas produced.

Question 9

Method for measuring effect of surface area on rate of reaction, using marble hips and HCl acid?

Answer 9

Measure volume of gas produced using gas syringe and take readings at regular time intervals and record results. Repeat experiment but with smaller but same mass marbles.

Question 10

3 factors that affect rate of reaction and which level of factor (e.g. higher or lower) will make rate of reaction faster?

Answer 10

• Greater surface area of reactants means faster rate
• Higher concentration means faster rate
• Higher temperature means higher rate

Question 11

Method to see effect of temperature on rate of reaction?

Answer 11

Heat both sodium thiosulfate and HCl acid. Mix solutions in conical flask over ‘X’ on paper and time for precipitate to form and obscure mark. Repeat but with different temperatures.

Question 12

How would you find the gradient of a curve on a graph?

Answer 12

Draw a tangent