Unit 6: Chemical Kinetics ; (HL) Topic 16.1 Rate expression and Rate Mechanism Flashcards
What are Rate equations?
experimentally-determined equations
what does the rate equations relate the rate of reaction to?
it relates the rate of reaction to the concentrations of substances in the mixture.
what is Rate Constant(K)?
a constant of proportionality
what does the rate constant relate the concentrations in the experimentally-determined rate expression to?
it relates the concentrations in the experimentally-determined rate expression to the rate of a chemical reaction.
The rate constant is only a constant for…
a particular reaction at a particular temperature.
what is the order of reaction?
the power of the reactant’s concentration in the experimentally-determined rate equation.
what is the order of a reaction always with respect to?
a particular reactant
what is the Individual order?
The power to which a concentration is raised in the rate equation
what is the Overall order?
The sum of all the individual orders in the rate equation
in the rate equation r = k[A][B]2
the order with respect to A is?
the order with respect to B is ?
the overall order is?
the order with respect to A is 1 1st Order
the order with respect to B is 2 2nd Order
the overall order is 3 3rd Order
The value is zero if the rate is…
unaffected by how much of a substance is present.
The units of k depend on what?
the overall order of reaction.
r = k[A] k will have units of?
r = k[A]^2 k will have units of?
r = k[A][B]^2 k will have units of?
r = k[A] k will have units of sec^-1
r = k[A]2 k will have units of dm^3 mol^-1 sec^-1
r = k[A][B]2 k will have units of dm^6 mol^-2 sec^-1
how can the rate equation be determined?
the rate equation can only be determined from experimental data.
what is the connection between the chemical equation for a reaction and the rate equation?
there is none
write a standard answer to the question: write the individual orders for A and B
When [B] is kept constant [A] is — (e.g. tripled). The rate also — (e.g. triples) (2 to 6). Therefore rate ∝ [A], so the order of reaction with respect to A is 1.
When [A] is kept constant [B] is — (e.g. doubled). The rate — (e.g. quadruples) (2 to 8). Therefore rate ∝ [B]^2, the order of reaction with respect to B is 2.
write a standard answer to the question: what is the overall order of reaction?
The overall order is the sum of the individual orders
= (e.g.) 1 + 2 = 3
write a standard answer to the question: what is the rate equation?
By combining the two proportionality relationships you can construct the overall rate equation;
therefor rate = k[A][B]
how can the variation in rate be investigated using a graph?
by measuring the change in concentration of one of the reactants or products, plotting a graph, and then finding the gradients of the curve at different concentrations.
the rate reaction at any moment can be found from the…
gradient of the tangent at that point.
if the gradient is steeper, what can you conclude?
the rate of reaction is faster
the order of reaction can be found by measuring what?
the rate at different times during the reaction and plotting the rate against either concentration or time.
what is the shape of a curve for zero order? (concentration vs time)
a straight line showing a constant decline in concentration
what is the shape of a curve for first order? (concentration vs time)
A slightly sloping curve that drops with a constant half-life
what is the shape of a curve for second order? (concentration vs time)
the curve steeply declines at first then levels out.
what is the shape of a curve for zero order? (rate of reaction vs concentration)
the rate does not depend on the concentration. The line is parallel to the x-axis.
what is the shape of a curve for first order? (concentration vs time)
the rate is proportional to the concentration so you get a straight line of fixed gradient. The gradient of the line equals the rate constant for the reaction.
what is the shape of a curve for second order? (rate of reaction vs concentration)
the rate is proportional to the square of the concentration. You get an upwardly sloping curve.
