STUDENT SPACE · TOPIC 1

Measuring reaction rates

Measure change over time and interpret a reaction curve.

The essentials

Rate measures the amount of reactant used or product formed per unit time.
A gas syringe measures the hydrogen from magnesium and dilute hydrochloric acid.
The curve is steepest near the start, so the reaction is fastest then.

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

A gas volume rises from 20 to 32 cm³ between 10 and 30 s. Calculate the interval rate.

Need a hint for Question 1?

Mark two times and their volumes before subtracting. Use the interval, not the time since zero.

Check Question 1

(32 − 20) ÷ (30 − 10) = 0.60 cm³ s⁻¹.

A reaction makes 36 cm³ of gas in 30 s. Calculate its average rate.

Need a hint for Question 2?

Divide change in volume by elapsed time.

Check Question 2

36 ÷ 30 = 1.2 cm³ s⁻¹.

The collected gas volume stops increasing. Explain what a horizontal section means.

Need a hint for Question 3?

A horizontal line has zero gradient.

Check Question 3

No additional gas is collected; the rate of gas production is zero if the apparatus is working correctly.

Use Lesson 1 in your worksheet for written practice. Your teacher will discuss those answers in class.