What is the definition for the rate of reaction?
The change in concentration of a reactant or product per unit time.
What is the order of the reatction?
The order resepct to a reactant is the power to which the concentration of the rate is raised in the rate equation.
What is 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 equations.
Give the definition for the rate equation.
for a reaction A + B -> C is given by: rate = k[A]m[B]n where m is the order of a reaction with respect to A and n is the order of reaction with respect to B.
Give the definition for the overall order.
The overall order of a reaction is the sum of the individual orders, n + m
What is the equation for measuring rates of reaction?
rate of reaction = change in concentration of reaction or products / time
What are the units for the ROR?
measured in moldm-3s-1, but if more appropriate moldm-3min-1.
How can you measure change in concentration to calculate the ROR?
Concentration is difficult to measure, measuring mass change or gas volume prodcued is usually easier.
How is the effect of individual reactants on the ROR described?
If more than one reactant is involved in a reaction, each reactant can affect the rate of the reaction differently. The effect of the individual reactants is decribed by stateing an order with respect to each reactant.
How do you express the effect of reactant A (its concentration affects the ROR) on the ROR?
rate(insert symbol for proportional)[A]x
What is a zero order reaction.
rate = [A]0
- The rate is unaffected by changing the concentratio of A.
- Note that any number to the power of O is equal to one.
What is a first order reaction?
rate = [B]1
- If [B] increases by two time, the rate increases by two times.
- If [B] invcreases by three times the rate increases by three times.
What is a second order reaction?
rate = [C]2
- If [C] increases by two times the rate increases by 22
- If [C] increases by three times the rate increases by 32 = 9 times.
How does expression for the effect of concentration of a reaction become a rate equation?
The sign for proportional can be removed if a constant is added into the equation. Chemists use the rate constant K. The rate constant links the concentrations and orders of reactants to the rate. The expression then becomes the rate equation.
rate = k[A]x[B]y[C]z
What reactants are not included in the rate equation?
If a reactant is 0 order it is not included in the rate equation.
How would you present a 0, 1st, and 2nd order reactant in a rate equation, if the reactants were A, B and C?
rate = k[B]1[C]2
What is the overall order for the reaction rate = k[B]1[C]2 ?
How do you calculate the value for a rate constant?
The rate constant is calculated by submitting values for concentration and rates into the rate equation and rearranging to find k.
Zero order, rate = k[A]0
k = rate/1
How do you calculate rate constants for a first order reaction?
rate = k[A]
k = rate/[A]
How do you calculate rate contants for a second order reaction?
rate = k[A]2
k = rate/[A]2
How do you work out the units for the rate constant, k?
The units of K depend on the verall order of the rate reactiion. The units of k are determined by substituting units for rate and concentration into the rate equation.
What will be the units of k for a zero order reaction, k = rate/1?
What will be the units of k for a first order reaction, rate = k[A]?
units of k = (moldm-ss-1) / (mol dm-3)2 = s-1
How would you calculate the rate constant for a third order reaction?
rate = k[A]2[B]
k = rate / [A]2[B]
What are the units for a rate constant of a third order reaction?
units of k = moldm-3s-1 / (mol dm-3)3 = dm6mol-2s-1
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 experimental rechniques may chemists use to measure the concentration of reactants or prodcts in a reaction.
Acids and bases
- PH changes carrying out titrations
- PH changes by using a PH meter
Reactions that produce gasses
- The change in volume or pressure
- the loss of mass of reactants
Reactions that form visual changes
- The formation of a precipitate
- A colour change. (colorimeter)
How can the rate of a reaction be found by using a concentration/time graph?
The rates of reaction can be founf by plotting the concentration on a coc tome graph and taking the gradient of a tangent/ (y/x).
What symbol is given for the half life of a reaction?
Half life is given the symbol t 1/2
Draw a zero order conentration time graph.