Rate of reaction
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Define 'rate of reaction'.
Rate of reaction is the change in concentration of a reactant or product per unit time. It's usually expressed in mol dm⁻³ s⁻¹.
Explain the relationship between frequency of collisions and the rate of reaction.
The rate of reaction is directly proportional to the frequency of collisions. A higher frequency of collisions (more collisions per unit time) generally leads to a faster rate of reaction, assuming the collisions also have sufficient energy.
What is the difference between an 'effective collision' and a 'non-effective collision'?
An effective collision results in a chemical reaction because the colliding particles have sufficient energy (activation energy) and proper orientation. A non-effective collision does not result in a reaction due to insufficient energy or incorrect orientation.
How does increasing the concentration of reactants affect the rate of reaction, in terms of collisions?
Increasing the concentration increases the number of reactant particles per unit volume. This leads to a higher frequency of collisions, and thus, a faster rate of reaction because there are more opportunities for effective collisions to occur.
Explain the effect of increasing pressure on the rate of reaction for gaseous reactants.
Increasing the pressure of gaseous reactants increases the concentration of the gases. This leads to a higher frequency of collisions, resulting in an increased rate of reaction.
Describe how to calculate the rate of reaction from experimental data measuring the change in concentration of a reactant over time.
The rate of reaction can be calculated as the change in concentration (Δ[reactant]) divided by the change in time (Δt): Rate = -Δ[reactant]/Δt. The negative sign indicates the reactant concentration is decreasing.
Define 'activation energy'.
Activation energy (Eₐ) is the minimum amount of energy required for a reaction to occur between colliding particles. It is the energy needed to overcome the energy barrier to form the activated complex.
Explain qualitatively the effect of increasing temperature on the rate of reaction, in terms of effective collisions.
Increasing temperature increases the average kinetic energy of particles. This results in more collisions and a greater proportion of collisions having energy greater than or equal to the activation energy, leading to a significant increase in the frequency of effective collisions and the rate of reaction.
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