R2.2 Measuring Rates of Reaction

Which experimental methods could be used to observe the progress of the following reaction?

Cr₂O₇^2-(aq) + 6I^-(aq) + 14H⁺(aq) → 2Cr³⁺(aq) + 3I₂(aq) + 7H₂O(l)

I. Change in colour

II. Change in mass

III. Change in electrical conductivity

• I and II

• I and III

• II and III

• I, II and III

Which variable is best to use when determining the rate of reaction for the decomposition of hydrogen peroxide?

2H₂O₂(l) → 2H₂O(l) + O₂(g)

• Volume of Solution

• Volume of Gas

• Change in absorbance

• Conductivity of Solution

Which is a correct unit for expressing the rate of a reaction?

• mol dm⁻³ s⁻¹ or M/s

• mol dm⁻³ s or M ∙ s

• mol ∙ s

• mol⁻¹ dm³ s⁻¹ or (mol ∙ L)/s

What is the rate of reaction? You have 2 minutes to get your data and use a calculator. After you do your calculation, choose the answer that is closest to your estimation.

• +135 M/s (or mol dm^-3 s^-1)

• • -135 M/s (or mol dm^-3 s^-1)

• • + 0.0074 M/s (or mol dm^-3 s^-1)

• • - 0.0074 M/s (or mol dm^-3 s^-1)

The rate of the acid-catalysed iodination of propanone can be followed by measuring how the concentration of iodine changes with time.

I₂(aq) + CH₃COCH₃(aq) → CHC₃OCH₂I(aq) + H⁺(aq) + I^-(aq)

Suggest how the change of iodine concentration could be followed.

• Color change

• Mass Change

• Volume of Gas

• Volume of Solution

CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)

Which methods can be used to monitor the progress of the reaction?

I. Change in colour of this reaction mixture

II. Change in mass of this reaction mixture

III. Change in volume of gas evolved

• I and II only

• I and III only

• II and III only

• I, II and III

100 cm³ of 10% hydrogen peroxide solution decomposes at 298 K to form water and oxygen.

H₂O₂ (aq) → H₂O(l) + ½O₂(g)

The dotted line graph represents the volume of oxygen produced. Which graph represents the decomposition of an equal volume of a 20% solution under the same conditions?

• A

• B

• C

• D

Excess magnesium powder was added to a beaker containing hydrochloric acid, HCl (aq). Which change could give line II?

• Doubling the mass of powdered Mg

• Using the same mass of Mg ribbon

• Increasing the temperature

• Using the same volume of more concentrated HCl

The curve shows the volume of gas from a chunk of metal reacting with excess acid. Draw a curve showing how it would look if the same mass of powdered metal was used instead. Ask your teacher to check your answer before you submit.

What was the average rate of reaction for reactant A for the first 7 minutes of the reaction?

• • - 0.020 M/s (mol dm^-3 s^-1)

• • - 0.0014 M/s (mol dm^-3 s^-1)

• • - 0.0057 M/s (mol dm^-3 s^-1)

• • - 0.0043 M/s (mol dm^-3 s^-1)