Chemistry 18 - Kinetics 2 Questions & Answers
What are the main factors that affect reaction rate?
Temperature, concentration (solutions), pressure (gases), surface area (solids), catalysts.
What is the rate of reaction?
The change in concentration of any of the reactants or products with...
Chemistry 18 - Kinetics 2 Questions &
Answers
What are the main factors that affect reaction rate? - answer Temperature,
concentration (solutions), pressure (gases), surface area (solids), catalysts.
What is the rate of reaction? - answer The change in concentration of any of the
reactants or products with unit time.
Usually it is assumed that a rate is measured by following the concentration of a
product, because the concentration of the product increases with time.
How does the rate of reaction change over time? - answer Initially the rate of
reaction is at its fastest, as there is a high concentration of reactant being formed into
product. As the amount of product increases and the amount of reactant decreases, the
rate of reaction slows as there is less product being formed. Eventually the rate of
reaction will level off once all of the product has been formed from all of the reactant.
How do you measure the rate of reaction at any instant? - answer Draw a tangent to
the curve at a specific time and then find its gradient (change in y/change in x)
What is the unit for rate of reaction? - answer mol dm⁻³ s⁻¹
What are the two different ways of measuring rates of reaction? - answer Monitoring
over time and end-point measurements
What methods could you use for monitoring over time? - answer > Measuring the
concentration/mass/volume of a product/reactant over time.
> Using a gas syringe to measure the volume of a gas formed over time.
What methods could you use for end-point measurements? - answer > Time taken
for an 'X' to disappear
> Time taken for a solid to dissolve
> Time taken for a colour change to occur
What does the rate of a chemical reaction depend on? - answer The concentrations
of some or all of the species in the reaction vessel (reactants and catalysts). These do
not necessarily all make the same contribution to how fast the reaction goes.
What is the rate equation? - answer An equation that describes how the rate of
reaction at a particular temperature depends on the concentration of species involved in
the reaction.
, It only tells us about the contribution of the species that DO affect the rate of reaction. It
is possible that one or more of the species that appear in the chemical equation will not
appear in the rate equation and vice versa (e.g. catalysts)
How do you find rate equations? - answer From experiments only.
How do you write a rate equation? - answer rate = k[A]ᴹ[B]ᴺ
where:
> k is the rate constant. This is different for every reaction and varies with temperature.
> [A] is the concentration of reactant A
> [B] is the concentration of reactant B
> M is the order of reaction with respect to A
> N is the order of reaction with respect to B
What is the order of a reaction? - answer The power to which the concentration of a
reactant must be raised to give the experimentally observed relationship between
concentration and rate.
It tells us how the rate depends on the concentration of that species.
What is the overall order of a reaction? - answer The sum of the orders of all the
species that appear in the rate equation (M+N)
What is a zero order reaction (w.r.t a species)? - answer A reaction where rate ∝
concentration⁰
This means that the rate is constant and independent of the concentration of the
reactant (increasing the concentration of the reactant has no effect on the rate).
A zero order reactant does not appear in the rate equation.
What is a first order reaction (w.r.t a species)? - answer A reaction where rate ∝
concentration
This means that doubling the concentration of the reactant will double the rate of
reaction.
What is a second order reaction (w.r.t a species)? - answer A reaction where rate ∝
concentration²
This means that doubling the concentration of the reactant will increase the rate of
reaction by a factor of 4.
What are the units of k for a zero order reaction? - answer rate = k
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