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.
whats the equation for rate?
rate = change in concentration / time
What is rate measured in?
Mol dm^-3 s^-1
what does zero order mean?
rate ∝ [A]°
rate is NOT affected by concentration
what does first order mean?
rate ∝ [A]¹
rate changes by the same factor as concentration
so if concentration doubles as does rate
what does second order mean?
rate ∝ [A]²
rate changes by the factor concentration does squared
if [A] doubles rate quadruples
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.
what is the overall order?
if two reactats A and B with orders m and n
the overall order = m+n
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.
what does a zero order and first order concentration time graphs look like?
what is a half life?
a half life of a reactant is the time take for its concentration to decrease by half.
a first order reaction has a constant half life
What are the two ways of continuous monitoring when a gas is produced?
the two ways of monitoring are
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.
the Arrhenius equation is found on the data sheet what do the symbols stand for?
k = A x e^(-E(a)/RT)
k = A x e^(-E(a)/RT) A - pre exponential factor -E(a)/RT - exponential factor R=gas constant= 8.314 T= temp in kelvin ea=activation energy
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|=-E(a)/R 1/T +ln|A|
Y= m X + c
ln[A] is the y intercept and -E(a)/RT ia the gradient
whats the equation for rate?
rate = change in concentration / time
what does the rate concentration graphs of zero, first and second order look like? explain there shapes
zero order
rate∝ [A]^0 therefore rate= constant
first order
rate∝[A]¹ so a linear shape upwards
second order
rate∝[A]² so curve upwards
