Topic 6: Kinetics Test Correction

Which one of the following factors does not affect the rate of a chemical reaction?

• The enthalpy change of the reaction
• The nature of the reactants (Nature means Orientation)
• The concentration of the reactants
• The presence of a catalyst

The rates of many reactions approximately double with a temperature increase of 10˚C. This is best attributed to a doubling of the fraction of molecules that have the energy needed for reaction.

Reactions between aqueous solutions of sodium thiosulfate and acid can be followed by timing the appearance of the solid sulphur that is produced. The time required for the appearance of the sulphur would be increased by which of the following changes?

·        Raising the temperature

·        Diluting the solution (this is because of the appearance of the solid sulphur)

·        Adding a catalyst

·        Increasing the concentration of the sodium thiosulfate

Define what is meant by the rate of reaction. Describe how the rate changes with time for the above reaction, and explain your answer using the Collision Theory:

·        Rate decreases as time increases.

·        The more concentrated the reactants, the more collisions there will be per second per unit volume.

·        As reactants get used up, concentration decreases.

·        This is why rate greatest at start rather than at the end.

·        Exothermic reaction therefore heat given out will also speed up reaction rate due to increasing collision frequency. Also kinetic energy of particles > E_a.