Chapter 18 - Rates of Reactions Flashcards
Orders, rate equations and rate constants, Concentration-time graphs, Rate-
What is a reaction’s rate?
The change in concentration per second.
What is rate measured in?
Mol dm^-3 s^-1
In a chemical reaction, if A is zero order, what effect would be seen if [A] is doubled?
Reaction rate would not change.
In a chemical reaction, if A is first order, what effect would be seen if [A] is doubled?
Reaction rate would double.
In a chemical reaction, if A is second order, what effect would be seen if [A] is doubled?
Reaction rate would quadruple.
How is the reaction rate at a specific time worked out using a concentration against time graph?
At the set time, draw a tangent to the curve and measure the gradient to get the rate.
If there are two reactants, A and B, what would be the rate equation?
rate = k x [A]^m x [B]^n
k - rate constant
m - order of A
n - order of B
What is initial rate?
The instantaneous rate at the beginning of an experiment when t=0.
In a concentration time graph, and a rate time graph, what would zero order look like?
Concentration time - linear to 0 concentration
Rate time - Horizontal line
In a concentration time graph, and a rate time graph, what would first order look like?
Concentration time - curve getting closer to zero
Rate time - Linear proportional
In a concentration time graph, and a rate time graph, what would second order look like?
Concentration time - steeper curve
Rate time - proportional to x^2
What are the two ways of continuous monitoring when a gas is produced?
Gas collection
Mass loss
What is a way of utilising light to monitor rate?
Using a colourimeter.
Measuring the amount of light absorbed by a solution.
What is half life?
The time taken for half of a reactant to be used up.
In a concentration time graph, how can you deduce whether the reactant is first or second order?
Measure multiple half lives.
If the half life is constant, it is first order.
If the half life is increasing, it is second order.
If the rate is only affected by one reactant, which is first order, what is another way of determining the rate constant?
k = ln|2| / t(1/2)
What is a reaction mechanism?
A series of steps that, together, make up the overall reaction.
What is the rate determining step?
The slowest step in the reaction mechanism of a multi-step reaction.
Why does temperature affect the rate constant?
Increasing the temperature, increases rate of reaction and thus rate constant.
What is the Arrhenius equation?
k = A x e^(-E(a)/RT)
A - pre exponential factor
-E(a)/RT - exponential factor
What is the logarithmic form of the Arrhenius equation?
ln|k| = -E(a)/RT + ln|A|
What can the log form of the Arrhenius equation be modelled as?
A straight line graph in y=mx + c ln|k| is y -E(a)/R is m 1/T is x ln|A| is c
