Chemistry - Equilibria, Energetics and Elements - F325 - Rates, Equilibrium and pH (1) Flashcards
Define the rate of reaction.
The rate of reaction is the change in concentration of a reactant or product per unit time.
Collisions must have more energy than what for a reaction to take place?
Collisions must have more energy that the activation energy for a reaction to take place.
How can the proportion of molecules that exceed the activation energy be altered?
The proportion of molecules that exceed the activation energy can be altered by changing the temperature or by adding a catalyst.
What is the equation for the rate?
Rate = (change in concentration of a reactant or product) / (time taken for the change to take place) moldm-3s-1
Rate is plotted on a graph of what against what?
Rate is plotted on a graph of time against concentration.
To measure reaction rates involving acids or bases what can you measure?
Measure pH change usinf a pH meter or by titration.
To measure reaction rates involving the production of gases, what can be measured?
Measure the change in volume or pressure or loss in mass of reactants.
To measure reaction rates that produce visual changes, what can be measured?
Can observe the formation of a precipitate or a colour change.
If the order is 0 with respect to reactant A, then how does changing the concentration of A affect the rate?
If the order is 0 with respect to reactant A then the rate is unaffected by changing the concentration of A.
If the order is 1 with respect to reactant A, then how does changing the concentration of A affect the rate?
If the order is 1 with respect to reactant A then if A increases 2 times the rate will also increase by 2 times.
If the order is 2 with respect to reactant A, then how does changing the concentration of A affect the rate?
If the order is 2 with respect to reactant A then if A increases by 2 times, the rate will increase by 4 times.
What would be the rate equation for the reaction A + B –> C ?
The rate equation would be:
rate = [A]^m[B]^n
where m is the order of reaction with respect to A
n is the order of reaction with respect to B
What is the overall order of reaction?
The overall order of reaction is the sum of the individual orders.
What does the rate constant, k, link the rate of reaction with?
The rate constant, k, is the constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation.
What is the half life of a reactant?
The half life of a reactant is the time taken for the concentration of the reactant to reduce by half.
What is the half life of a first order reaction?
A first order reaction has a constant half life. The half life is the same no matter what the concentration is.
What is the half life of a zero order reaction?
A zero order reaction, the concentration decreases at a constant rate, the half life decreases with time.
What is the half life of a second order reaction?
For second order reactions, the concentration decreases rapidly but the rate of decrease then slows down. The half life increases with time.
What shape is a rate-concentration graph for a zero order reaction?
Flat horizontal line.
The rate is unaffected by changes in concentration.
What shape is a rate-concentration graph for a first order reaction?
Linear relationship.
If the concentration of A doubles, then so does the rate.
What shape is a rate-concentration graph for a second order reaction?
Quadratic relationship.
If A increases by 2 times then the rate increases by 4 times.
How is the initial rate calculated?
To calculate the initial rate, draw a tangent from t=0 or a clock reaction.
A fast reaction will have a …….. value of k.
A fast reaction will have a large value of k.
A slow reaction will have a ………….. value of k.
A slow reaction will have a small value of k.
What is the rate-determining step?
The rate-determining step is the slowest step in the reaction mechanism of a multi-step reaction.
How do you know a reactant is involved in the rate determining step?
If a reactant appears in the rate equation, the reactant is involved in the rate-determining step.
What is a dynamic equilibrium?
A dynamic equilibrium is established in a closed system when the rate of the forward reaction is the same as the rate of the reverse reaction and the concentrations of the reactants and products remains the same.
What is Kc?
Kc is the equilibrium constant in terms of concentrations.
The equilibrium law states that for the equation aA + bB cC + dD, Kc = ?
Kc = [C]^c[D]^d / [A]^a[B]^b
Define a homogeneous equilibrium.
A homogeneous equilibrium is an equilibrium in which all the species making up the reactants and products are in the same physical state.
Define a heterogeneous equilibrium.
A heterogeneous equilibrium is an equilibrium in which species making up the reactants and products are in different physical states.
The magnitude of Kc indicates what?
The magnitude of Kc indicates the extent of a chemical reaction.
What does a Kc value of 1 indicate?
A Kc value of 1 indicates that the position of equilibrium is halfway between the reactants and the products.
What does a Kc value greater than 1 indicate?
A Kc value greater than 1 indicates that the reaction is product favoured.
What does a Kc value less than 1 indicate?
A Kc value less than 1 indicates that the reaction is reactant favoured.