3C - rates of reaction Flashcards
What is the definition of “Rate of Reaction?”
The change in concentration of a reactant or product in a given time.
What is the formula for Rate of Reaction?
Rate = Change in Concentration / Time
Fill the gaps: “Particles must collide in the correct _____ and with
sufficient energy to overcome ______ ______ for a reaction to
occur.
Orientation, Activation Energy
Particles must collide in the correct Orientation and with sufficient energy to overcomem Activation Energy for a reaction to
occur.
Name five things that could increase the rate of reaction.
Increasing the concentration of reactant, Increase the
temperature, change pressure (of gases in the reacting system),
Increase the surface area (of solid reactants) and catalyst
How does increasing the surface area of a solid reactant increase
the frequency of collisions?
By increasing the surface area of a solid reactant, a greater
number of particles on the reactant surface are able to react,
increasing the frequency of collisions.
At a set temperature, do all particles have the same kinetic
energy?
No, at a given temperature, the particles will have a range of
different speeds. unless absolute zero
Why must the Boltzmann curve pass through the origin?
Because there are no particles with no energy
What does the area under the Boltzmann curve represent?
The total number of particles
What is a catalyst?
A substance that increases the rate of a chemical reaction
without being used up in the process. A catalyst provides an
alternative route with a lower activation energy.
What is a homogeneous catalyst? Give an example
A catalyst that is in the same physical state as the reactants.
H2SO4 in making esters
What is a heterogeneous catalyst? Give an example
A catalyst that is in a different physical state as the reactants
Ni(s) in electrophilic addition of H2 (g) to an alkene
When measuring the rate of a reaction, measuring the gas
produced with a gas syringe may not be appropriate, even in
reactions where gases are produced. Why is this the case?
The gas could be soluble in the solution, so the measured volume
of gas produced by the gas syringe will not be equal to the actual
volume of gas produced.
Why is using a pH probe to measure changes in pH often not
recommended to measure rate of reaction?
Because pH is a logarithmic scale, changes in pH often aren’t
significant enough to be a good measurement of rate of reaction
On a concentration time graph, describe briefly how to find
instantaneous rate at a given time, t.
Take a tangent at the time = t. Find the gradient of the tangent
(this can be done by drawing a triangle to find x and y dimensions,
and then divide y by x to find the gradient).
List four ways that rates of reaction can be monitored in a lab.
- Measure the volume of gas produced using a gas syringe /
upturned measuring cylinder - Measuring the mass lost as gas is produced using a mass
balance. - Measure the change in absorbance value as a colour change
occurs using a colorimeter. - Measure the change in conductivity (due to total ion content
changes) can be measured using a conductivity probe.
