IB Chemistry HL - Unit 6 Chemical kinetics
The rate determining step of a chemical reaction has the highest (1) energy of all the (2) steps.
(1) - activation (2) - elementary
For a chemical reaction to occur, chemical species must (1) at a specific (2) with sufficient (3).
(1) - collide (2) - orientation (3) - energy
The rate of a reaction is proportional the the (1) of the (2).
(1) - concentration (2) - reactants
Determining the order of a reaction can only be done (1).
(1) - experimentally
First order reactions have a constant (1).
(1) - half-life
A unimolecular reaction involves (1) reactant species.
(1) - one
In a chemical reaction occurring in multiple steps, the (1) step determines the rate of reaction.
(1) - slow
The order of a reaction is equal to the (1) of the (2) of the reactants.
(1) - sum (2) - orders
A termolecular reaction involves (1) reactant species.
(1) - three
A bimolecular reaction involves (1) reactant species.
(1) - two
Define what is meant by a "reaction mechanism".
A reaction mechanism refers to the different elementary steps which occur to complete a chemical reaction.
What effect does a 10ºC increase in temperature have on the rate of a chemical reaction?
A temperature increase of 10ºC approximately doubles the rate of a chemical reaction.
Define what is meant by an "intermediate" species in a chemical reaction.
An intermediate species refers to a chemical species produced by an elementary step which is used as a reactant in a later elementary step, and is therefore not given out as a final product.
State the Arrhenius equation.
Arrhenius equation:
State the Arrhenius plot equation.
Arrhenius plot equation: Derived by taking the natural logarithm of both sides of the Arrhenius equation.
Explain how adding a catalyst to a chemical reaction affects rate of reaction.
Catalyst effect on rate of reaction: - Catalyst provides reactants with alternate reaction pathway with lower activation energy - Lowering activation energy gives more reactants kinetic energy ≥ activation energy → more successful collisions, increased rate of reaction
Explain how increasing concentration of the reactants affects rate of reaction.
Concentration effect on rate of reaction: - Increasing concentration → more particles, increased likelihood of collision - More successful collisions → increases rate of reaction
Describe how to determine the order of a reaction experimentally.
Determining rate of reaction experimentally: - Change concentration of a reactant - If rate does not change, order of reaction with respect to the reactant is 0 - If rate change is directly proportional to concentration, order of reaction with respect to the reactant is 1 (eg doubling [A] causes rate of reaction to increase by factor of 2 - If rate of change is the square value of the change in concentration of the reactant, order of reaction with respect to the reactant is 2 (eg tripling [A] rate of reaction to increase by factor of 9)
Give the units of k for a reaction with an order of 1.
First order: rate = k[A] units of rate/units of concentration s⁻¹
Explain how increasing pressure of gaseous reactants affects rate of reaction.
Pressure effect on rate of reaction of gaseous reactants: - Increasing pressure → gaseous particles closer together, more likely to collide → more successful collisions, increased rate of reaction
State the formula to determine rate of reaction when given the change in the concentration of products.
Rate of reaction = (Change in concentration of products)/(Change in time) Rate of reaction = ∆[Products]/∆t
State the formula to determine rate of reaction when given the change in the concentration of reactants.
Rate of reaction = -(Change in concentration of reactants)/(Change in time) Rate of reaction = -∆[Reactants]/∆t
State the different methods used to determine rate of reaction.
Rate of reaction can be determined by measuring: - Rate of colour change (Colourimetry) - Change in mass (Mass balance)/Change in volume of gas (Gas syringe) - Change in electrical conductivity (conductivity meter) - Change in pH of solution (pH probe) - Clock reactions (Comparing times for observable change to occur)
Give the units of k of a reaction with an order of 2.
Second order: rate =[A]² units of rate/(units of concentration)² mol⁻¹ dm³ s⁻¹
Explain how increasing surface area of the reactants affects rate of reaction.
Surface area effect on rate of reaction: - Increasing surface area increases area for particles to collide and react → more successful collisions, increased rate of reaction
Explain how increasing temperature of the reactants affects rate of reaction.
Temperature effect on rate of reaction: - Increasing temperature increases average kinetic energy of particles → particles move more quickly, more likely to collide → more successful collisions, increased rate of reaction - Increasing temperature increases number of particles with kinetic energy ≥ activation energy → more successful collisions, increased rate of reaction
How does the rate of a first order reaction change with concentration?
The concentration of a first order reaction (rate = k[A] is directly proportional to the rate of the reaction (rate increases linearly with concentration)
How does the concentration of a first order reaction change with time?
The concentration of a first order reaction (rate = k[A]) decreases quickly at the beginning, before the rate of change decreases and the concentration levels off
How does the concentration of a second order reaction change with time?
The concentration of a first order reaction (rate = k[A]²) decreases rapidly at the beginning, before the rate of change quickly decreases and the concentration levels off
How does the concentration of a zero order reaction change with time?
The concentration of a zero order reaction (rate = k) decreases linearly with time.
How does the rate of a zero order reaction change with concentration?
The concentration of a zero order reaction (rate = k) has no effect on the rate of the chemical reaction.
What does the effect of temperature on the rate constant of a chemical reaction depend on?
The effect of temperature on the rate constant (k) of a chemical reaction depends on the activation energy of the reaction.
Define what is meant by the "molecularity" of a chemical reaction.
The molecularity of a chemical reaction refers to the number of reactant particles in the reaction.
What is the overall rate expression of a chemical reaction dependent on?
The overall rate expression of a chemical reaction is dependent on the rate expression of the slowest elementary step (rate determining step, slow step).
What does the rate constant (k) of a chemical reaction depend on?
The rate constant (k) of a chemical reactions is dependent on temperature.
How can the rate of reaction of a chemical reaction at a given time be determined from a graph?
The rate of a chemical reaction at a given time can be determined graphically by calculating the gradient of the tangent at the needed time.
Explain when the rate of a chemical reaction is highest.
The rate of a chemical reaction is highest at the beginning of the reaction, as there is the greatest concentration of the reactants at this time.
Briefly describe what is meant by the "rate of reaction".
The rate of a reaction refers to the change in the concentration of the reactants/products over given period of time.
How does the rate of a second order reaction change with concentration?
The rate of a second order reaction (rate = k[A]²) increases quadratically with an increase in concentration
Give the units of k of a reaction with an order of 3.
Third order: rate = [A]³ units of rate/(units of concentration)³ mol⁻² dm⁶ s⁻¹
Give the units of k for a reaction with an order of 0.
Zero order: rate = k units of rate mol dm⁻³ s⁻¹
What is the rate expression for the reaction A + B → C?
rate = k[A][B]
