Rate of reaction
the change in concentration of reactants or products per unit time
Collision Theory
a chemical reaction to take place, the particles need to collide with each other in the correct orientation and with enough energy
Collision Frequency
The number of collisions per unit time.
What increases the rate of reaction?
- higher concentration
- higher pressure
- high temperature
- catalyst
- higher surface area
Activation Energy
the minimum amount of energy required for a reaction to take place
Boltzmann distribution curve
a graph that shows the distribution of energies at a certain temperature
What happens to the Boltzmann distribution curve when the temperature increases?
the curve moves to right but the peak is lower than the original
Catalyst
a substance that increases the rate of a chemical reaction by lowering the activation energy without being consumed by offering an alternative pathway
Homogenous catalyst
the catalyst is in the same phase/state as the reactants
Heterogenous catalyst
the catalyst is in a different phase/state to the reactants
What is the formula for the rate equation?
k[P]^m[Q]^n
where m and n are the order of reaction
k is rate constant
and the others are concentrations
What is a elementary reaction?
a reaction which occurs in a single step
what is meant by the r.d.s?
rate determining step
the slowest step in the reaction which determines the rate of overall reaction
What does the order of a reactant show?
how the concentration of a reactant affects the rate of reaction
What does it mean when the order of reaction with respect to a substance is 0?
that changing the concentration of the chemical has no effect on the rate of reaction, therefore not included in the rate equation
What does it mean when the order of reaction with respect to a substance is 1?
the concentration of the substance is directly porportional to the rate of reaction, and is included in the rate equation
What does it mean when the order of reaction with respect to a substance is 2?
the rate is directly porportional to the square of the concentration of that substance, and it is included in the rate equation (to the power of 2)
What is the overall order of reaction?
the sum of the powers of the reactants in a rate equation
What is half-life?
the time taken for the concentration of a limiting reactant to become half of its initial value
What does the graph of a zero order reaction look like?
(for the conc of reactants against time graph)
a straight line with a negative gradient
How is the initial rate of reaction calculated?
the gradient of the curve at x=0
What happens to the half-life for zero, first & second order reactions?
explain separately
- HL for zero order is half
- HL for first order is constant
- HL for second order is doubled
What are the two commonly used methods for determining the order for reaction?
- titrimetry (titration method)
- colorimetry (measuring the colour intensity)
What is the process for titrimetry?
remove the sample –> quench (stop) –> titrate
