M5S1 – Kinetics 1

Which of these are examples of kinetic stability?

(i) A solution of hydrogen peroxide can be stored at room temperature

(ii) Hydrogen does not ignite in air at room temperature

(iii) Aluminium does not corrode in moist air

(iv) Magnesium oxide does not decompose on heating

An alloy of platinum with rhodium is the catalyst used:

(i) in catalytic converters to cut pollution from motor vehicles

(ii) in the synthesis of ammonia from nitrogen and hydrogen

(iii) in the oxidation of ammonia to NO_(g) during the manufacture of nitric acid

(iv) in the hydrogenation of vegetable oils.

Which of these statements about catalysts are true?

(i) A catalyst speeds up a forward reaction but slows down the reverse reaction

(ii) With a catalyst the enthalpy change for the reaction becomes more negative

(iii) With a catalyst the pathway for the reverse reaction has a higher activation energy

(iv) With a catalyst the pathway for the forward reaction has a lower activation energy

A Maxwell-Boltzman plot shows the distribution of molecular energies in a sample of gas at a 300K. The curve showing the distribution at 310K:

(i) has a wider spread,

(ii) has a higher peak,

(iii) has the peak shifted to the right,

(iv) has a larger area under the curve.

For which of these reactions can the rate of reaction be studied by collecting one of the products over water in a graduated tube (or measuring cylinder) inverted in a trough of water?

(i) Na₂SO_3(s) + 2HCl_(aq) -> 2NaCl_(aq) + SO_2(g) + H₂O_(l)

(ii) Zn_(s) + H₂SO_4(aq) -> H_2(g) + ZnSO_4(aq)

(iii) 2KCl_(s) + H₂SO_4(l) -> KHSO_4(s) + HCl_(g)

(iv) CaCO_3(s) + 2HNO_3(aq) -> Ca(NO₃)_2(aq) + CO_2(g) + H₂O_(l)

The activation energy for the reaction of sodium thiosulfate with acid is close to 50 kJ mol^-1. Mixing a measured volumes of sodium thiosulfate solution and hydrochloric acid at 30^oC produces a certain amount of sulfur in 120 seconds.

Repeating the experiment with all the conditions the same except the temperature is 40 ^oC produces the same amount of sulfur in:

When 0.08 g magnesium ribbon reacts with 50 cm³ of 2.00 mol dm^-3 hydrochloric acid the reaction produces 80 cm³ gas in 400 seconds at room temperature and pressure but then stops. On repeating the reaction under the same conditions with 0.08 g magnesium ribbon and 100 cm³ of 1.00 mol dm^-3 hydrochloric acid the outcome is that the reaction:

When a sample of calcium carbonate reacts with dilute hydrochloric acid, 144 cm³ of carbon dioxide form in 20 seconds at room temperature and pressure.

What is the rate of loss of hydrochloric acid in moles per second. (Volume of 1 mol gas under these conditions = 24 000 cm³)

Thiosulfate ions react with acid to produce a precipitate of sulfur. The following volumes of sodium thiosulfate solutions are mixed in separate small flasks with 10 cm³ samples of 2.0 mol dm^-3 hydrochloric acid together with enough water to make the total volume 50 cm³.

In which flask does the precipitate of sulfur form fastest?

The activation energy for the reaction of H_2(g) with I_2(g) is 120 kJ mol^-1. The standard enthalpy change for the reaction is +53 kJ mol^-1.

What is the activation energy for the decomposition of hydrogen iodide into its elements?