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Topic 6 and Topic 16 Chemical Kinetics
Terms in this set (19)
Rate of Reaction
Increase in concentration of products or decrease in concentration of reactants per unit time. Rate usually decreases with time because reactant is used up.
Displays the distribution of kinetic energies of particles in a liquid or gas. KE is x-axis, and the more KE the faster they move. Number of particles is y-axis, which has a large peak and then slowly decreases. Area beneath graph doesn't change because number of particles remains the same, so the curve becomes less sharp as temperature increases because more particles have a higher kinetic energy.
1. Particles must collide. 2. Must collide with correct orientation/geometry. 3. Must collide with sufficient energy.
The minimum amount of energy required to initiate a collision/reaction.
Effect of Temperature
Particles move faster with higher temp (higher KE), so more frequent collisions will occur. With higher KE, more colliding particles will also have sufficient activation energy for more successful collisions.
Effect of Surface Area
For solids, only particles on surface can participate in reactions. Increasing surface area increases number of participating particles, which results in more frequent collisions.
Effect of Catalyst
Catalysts provide an alternate pathway for a reaction with a lower activation energy. With a lower activation energy, more particles will have sufficient energy for successful collisions. Catalyst is not chemically changed during the reaction.
Effect of Concentration
More concentration means more reactant per volume, so there are more frequent collisions.
Rate Constant (and expression)
Reaction rates found experimentally and are proportional to the concentration of a reactant raised to a power.
Rate=k[A]^x[B]^y, where k is the rate constant.
x is the order of the reaction with respect to A and y is the order of the reaction with respect to B. The overall order of the reaction is x+y.
The rate constant is dependent on temperature.
Zero Order Reaction
[A] vs time graph is a negative linear function (gradient is constant, k) and rate vs [A] graph is straight line of gradient 0.
First Order Reaction
Rate=k[A]; k in s⁻¹
[A] vs time graph is negative and curved, similar to quadratic, and rate vs [A] graph is a straight upwards line (the higher the concentration, the higher the rate, but changes linearly because [A] only used once in rate equation).
Second Order Reaction
Rate=k[A]² or rate=k[A][B]; k in dm³mol⁻¹s⁻¹
[A] vs time graph is negative and more curved than in a first order reaction, and rate vs [A] graph is curved upwards (a graph of rate vs [A]² would be linear).
Time taken for the concentration of a reactant to fall to half of its initial value. First order reactions have a constant half-life.
The slowest step in a reaction mechanism, and hence determines the rate. The species involved in the RDS define the rate expression.
One species involved in an elementary step (a single species breaks down into two or more products).
Two species involved in an elementary step (two species collide together)
The products of when species with the necessary activation complex collide in a bimolecular step. It cannot be isolated, and either breaks down to form the products or reverts back to the original reactants.
Usually refers to the number of reacting species in the rate determining step.
Relates temperature to the rate constant of a reaction. As the temperature increases, the rate constant increases because the rate increases with temperature.
Ea is the activation energy; R is the gas constant; T is in Kelvin; A is the frequency factor, which is the the frequency of collisions with the correct orientation for the reaction.
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