Chapter Three · Factors affecting the rate of chemical reactions: practice questions

Which of the following is NOT one of the factors affecting the rate of a chemical reaction?

• ANature of the reactants
• BMagnetic field
• CCatalysts
• DLight

A catalyst increases the rate of a chemical reaction because it:

• Aprovides an alternative pathway of lower activation energy
• Bincreases the concentration of the reactants
• Cincreases the activation energy of the reaction
• Draises the temperature of the reactants

The activation energy of a reaction is:

• Athe total kinetic energy of all the reactant molecules
• Bthe minimum amount of energy that must be gained by a molecule to react at collision
• Cthe energy released when the products are formed
• Dthe difference in energy between the reactants and the products

What happens to the rate of many chemical reactions when the reaction temperature is increased by 10° C?

• AIt is halved
• BIt remains unchanged
• CIt becomes zero
• DIt is doubled

During a reaction, the concentration of a reactant decreased from 0.80 mol/L to 0.50 mol/L in 60 seconds. What is the average rate of disappearance of this reactant?

• A1.3 × 10⁻² mol/(L·s)
• B8.0 × 10⁻³ mol/(L·s)
• C5.0 × 10⁻³ mol/(L·s)
• D0.30 mol/(L·s)

Equal masses of metal (X) were added to identical portions of the same dilute acid at the same temperature: in flask (1) as a single block and in flask (2) as a fine powder. Which of the following correctly compares the two flasks?

• ABoth flasks react at exactly the same rate
• BThe reaction in flask (1) is faster because the block is denser
• CThe powder in flask (2) has a lower activation energy
• DThe reaction in flask (2) is faster because the powder offers a greater surface area for collisions

Raising the temperature of a reacting mixture increases the reaction rate. Which of the following is the principal reason for this large increase?

• AThe activation energy of the reaction is lowered
• BThe enthalpy change of the reaction becomes more negative
• CThe concentration of the reactants increases
• DA larger fraction of the molecules acquire an energy equal to or greater than the activation energy

In a gaseous reaction, the number of effective collisions per second determines the rate. Which single change would increase the collision frequency WITHOUT increasing the average energy of the molecules?

• Aincreasing the concentration (pressure) of the reacting gases at constant temperature
• Braising the temperature of the gas
• Clowering the activation energy of the reaction
• Dadding a catalyst

In the reaction 2SO2(g) + O2(g) -> 2SO3(g), at a certain instant SO2 is disappearing at 0.16 mol/L.s. Which of the following correctly gives the rate of disappearance of O2 and the rate of appearance of SO3?

• AO2 = 0.16 mol/L.s , SO3 = 0.16 mol/L.s
• BO2 = 0.32 mol/L.s , SO3 = 0.16 mol/L.s
• CO2 = 0.08 mol/L.s , SO3 = 0.16 mol/L.s
• DO2 = 0.08 mol/L.s , SO3 = 0.08 mol/L.s

For the decomposition 2N2O5(g) -> 4NO2(g) + O2(g), oxygen is produced at a rate of 0.024 mol/L.s. The rates of decomposition of N2O5 and of formation of NO2 are respectively:

• A0.096 mol/L.s and 0.048 mol/L.s
• B0.024 mol/L.s and 0.024 mol/L.s
• C0.048 mol/L.s and 0.096 mol/L.s
• D0.012 mol/L.s and 0.006 mol/L.s