Rates, equilibrium and pH

Define rate of reaction?

• The change in quantity of reactant or product per unit time

State the units of concentration?

• mol dm-3

What is meant by the order of a reaction?

• the power to which the concentration of a reactant is raised in the rate equation

State the reaction orders?

• Zero order

• First order

• Second order

What is a Zero order reaction with respect to A?

• Rate is independent of [A]

• Rate = [A]0

What effect does changing [A] have on rate in a zero order reaction?

• no effect

What is a first order reaction with respect to [A]?

• rate is directly proportional to [A]

• Rate = [A]1

If [A] doubles in a first order reaction, what happens to the rate?

• the rate doubles

If [A] triples in a first order reaction, what happens to the rate?

• The rate triples

What is a second order reaction with respect to [A]?

• Rate =[A]2

If [A] doubles in a second order reaction, what happens to the rate?

• the rate increase by 2 squared therefore rate = 4

If [A] triples in a second order reaction, what happens to the rate?

• The rate increases by 3 squared therefore rate = 9

What is the general rate equation for reactants A and B?

• Rate= k[A]m[B]n

What does k represent in the rate equation?

• The rate constant

What does the overall order of a reaction mean?

• the sum of all individual orders: m+n

State the 2 ways which the rate of reaction can be continuously measured?

• monitoring by gas collection

• Monitoring by mass loss

What does a colorimeter measure?

• the amount of light absorbed by a solution

What concentration graph does a zero order reaction produce?

• A straight line with a downward curve

What concentration graph does a first order reaction produce?

• a downward curve with a decreasing gradient

Define half life in terms of a first order reaction?

• the time taken for half of a reactant to be used up

What concentration graph does a second order reaction produce?

• A downward curve

Draw the rate- concentration graphs for zero order, first order and second order?

Define the initial rate?

• the rate at the start of the reaction where t=0

What type of reaction is a more convenient method to obtain the initial rate of a reaction?

• a clock reaction

What does a common clock reaction rely on?

• The formation of iodine

How do iodine clocks work?

• the time taken from the start of the reaction and the appearance of the iodine colour can be measured

Define stoichiometry?

• the relative amounts of the species in the reaction

What gives you the stoichimetry of a chemical reaction?

• the balancing numbers

Define the reaction mechanism?

• the series of steps which make up an overall reaction

Define the rate determining step?

• the slowest step in a multi step reaction

What happens to the value of k as temperature increases?

• k also increases

State the 2 factors which contribute to the increased rate and rate constant when temperature increases?

• shifts Boltzmann distribution to the right which increases the proportion of particles that exceed activation nervy

• Particles move faster and collide more frequently

What is the Arrhenius equation an exponential relationship between?

• the rate constant(k) and temperature (T)

What does the exponential factor represent?

• the proportion of molecules that exceed Ea and have sufficient energy for a reaction to take place