Average Rate of Reaction

The average rate of a chemical reaction can be calculated using which of the following formulas?

• Rate = concentration × time

• Rate = time ÷ change in mass

• Rate = change in quantity ÷ time

• Rate = temperature ÷ time

Which of the following units would be appropriate for the average rate of a reaction measured by change in mass?

• mol⁻¹ s

• g s⁻¹

• s mol⁻¹

• mol dm³

A reaction produced 60 cm³ of gas in 30 seconds. What is the average rate of reaction?

• 2 cm³ s⁻¹

• 0.5 cm³ s⁻¹

• 30 cm³ s⁻¹

• 1800 cm³ s⁻¹

In a rate calculation, the 'quantity' measured can be all of the following except:

• Volume of gas

• Change in concentration

• Change in mass

• change in particle size

A student measures the time taken to collect 100 cm³ of gas. What else is needed to calculate the average rate?

• Temperature of the gas

• Type of gas

• Concentration of acid

• The time in seconds

A graph of volume of gas produced (y-axis) against time (x-axis) is drawn. How is the average rate calculated?

• Measure the gradient at the final point

• Divide total volume by total time

• Multiply volume by time

• Subtract final time from initial time

A student calculates an average rate of 0.40 g s⁻¹. Which interpretation is correct?

• The reaction used 0.40 g of reactant per second

• The mass of the product increased by 0.40 g each second on average

• 0.40 g of gas escaped every second

• The concentration increased by 0.40 mol per second

A reaction produces 12.0 g of product in 3.0 minutes. What is the average rate in g s⁻¹?

• 0.25

• 4.0

• 36.0

• 0.067

Which of the following would give the most accurate value for the average rate?

• Measuring the total reaction time by estimation

• Using a stopwatch and measuring temperature

• Repeating the experiment and averaging results

• Estimating the change in concentration

Why is the average rate only an estimate of how fast the reaction occurs?

• The reaction is only measured at one time point

• The reaction rate changes over time

• Catalysts alter the total volume

• Reactants always change state