1.7 Kinetics

Curve 1 was produced from measuring the decomposition of 100 cm³ of 1.0 mol dm^–3 hydrogen peroxide in the presence of a manganese (IV) oxide catalyst.

Which alteration to the original experimental conditions would produce curve 2?

In a reaction between 1.00 mol dm^-3 hydrochloric acid and an excess of calcium carbonate chips, the volume of gas produced was measured against time. This is shown on the dotted line in the graph below.

The experiment was repeated, but this time using the same volume of 2.00 mol dm^-3 hydrochloric acid. 

Which line on the graph represents this experiment?

The diagrams below shows the Maxwell–Boltzmann distribution of molecular energies in a sample of gas.

In diagram 1, one line, P or Q, corresponds to the activation energy in the presence of a catalyst and the other line corresponds to the activation energy of the same reaction in the absence of a catalyst.

In diagram 2, one curve, X or Y, corresponds to a temperature higher than that of the other curve. 

Which combination gives the correct curve and line?

	Presence of catalyst	Higher temperature
A	P	X
B	P	Y
C	Q	X
D	Q	Y

In an experiment 1.0 mol dm^-3 H₂O₂ was reacted with hydrochloric acid at 20 C and the volume of oxygen recorded, as shown by curve 1.

The experiment was repeated a second time to produce curve 2.

What factor was changed to produce curve 2?

Hydrogen will react with chlorine to form hydrogen chloride gas.

Apart from increasing temperature, what other two factors could speed up the rate of hydrogen chloride formation?

	Heterogeneous catalyst	Increase the most probable energy, Emp	Increase pressure	Decrease pressure
A	✓	⨯	✓	⨯
B	✓	⨯	⨯	✓
C	⨯	⨯	⨯	✓
D	⨯	✓	✓	⨯

Which arrow indicates the activation energy for a catalysed reaction on the reaction profile shown?

Consider the Maxwell-Boltzmann distribution curve below.

What would be the effect on the distribution curve if the number of molecules in the original reaction mixture is increased, but no other changes are made?

	Area under the curve increases	Most probable energy, Emp increases	Number of molecules with energy ≥ Ea increases	Curve shifts upwards and to the left
A	⨯	✓	✓	⨯
B	✓	⨯	⨯	✓
C	✓	⨯	✓	⨯
D	⨯	⨯	✓	⨯

Consider the Maxwell-Boltzmann distribution of molecular energies for gaseous molecules, with and without a catalyst.

What would always result in a decrease in the number of molecules contained within area Y?

	Decrease pressure	Decrease temperature	Putting the gas into a smaller container	Removing a quarter of the catalyst
A	⨯	⨯	✓	⨯
B	⨯	✓	⨯	⨯
C	⨯	✓	⨯	✓
D	✓	✓	⨯	⨯

30.0 cm³ of 0.750 mol dm⁻³ aqueous ethanoic acid reacts with 390 mg sodium which is the limiting reagent. 

Hydrogen gas is produced and collected with a gas syringe.

What is the minimum mass, in mg, of sodium required to react?

The reaction pathway for an endothermic reaction is shown.

Which arrow represents the activation energy for the reverse reaction?

The dotted-line curve on each graph below represents the corresponding Maxwell-Boltzmann distribution for a gas at 200 K. 

Which solid-line curve most accurately represents the Maxwell-Boltzmann distribution of molecular energies in the same gas at 400 K?

The reaction pathway shows the energies of the reactants, the products and the transition state of a reaction.

Which expression correctly represents how to calculate the activation energy of the forward reaction?

The Maxwell-Boltzmann distribution of the kinetic energies of molecules in a slowly reacting gaseous mixture, without a catalyst, at a given temperature is shown. 

The activation energy for the reaction, E_a, is marked for the uncatalysed reaction.

What would the position of E_a be if the reaction took place with an effective catalyst?

Four possible reactions (A, B, C and D) of the following equation are measured at the same temperature.

X (g) + Y (g) → Z (g)

Which reaction pathway diagram shows the reaction occurring rapidly with an overall negative enthalpy value?

The diagram shows a Maxwell-Boltzmann distribution of molecular energies for a gaseous mixture. The distribution has a peak, labelled Q on the diagram.

What happens when an effective catalyst is added to the mixture?

The Maxwell-Boltzmann distribution of the distribution of molecular energies in sample 1 of a gas is shown.

A change was made to the reaction conditions, as shown by the dotted curve, labelled sample 2.

What factor was changed in the reaction conditions to produce the dotted curve, labelled sample 2? 

	Temperature increased	Catalyst added	Volume reduced
A	⨯	⨯	✓
B	⨯	⨯	⨯
C	✓	⨯	⨯
D	⨯	✓	⨯

A student performs two reactions and measures the rate of product formation. 

Reaction 1: 1.5 g of solid calcium carbonate is added to 100 cm³ of 0.5 mol dm^-3 hydrochloric acid.

Reaction 2: 100 cm³ of distilled water is added to 100 cm³ of 0.5 mol dm^-3 hydrochloric acid and then 1.5 g of solid calcium carbonate is added.

The rate of reaction 1 was faster than the rate of reaction 2. 

Which of the following 3 hypotheses correctly describes the difference in the rate as a result of adding water? 

	Frequency of collisions between reactant molecules is reduced	Proportion of effective collisions between reactant molecules is reduced	Proportion of reactant molecules possessing the activation energy is reduced
A	⨯	⨯	✓
B	✓	✓	⨯
C	✓	⨯	⨯
D	✓	✓	✓

The Maxwell-Boltzmann distribution shows the number of molecules that have particular kinetic energy at a constant temperature.

If the temperature is decreased by 10 C, what happens to the size of the areas labelled H, J and K?

	H	J	K
A	decreases	increases	decreases
B	decreases	decreases	decreases
C	increases	decreases	increases
D	increases	decreases	decreases