These are detailed Revision Notes for Topic 1.5 of AQA A-Level Chemistry (Kinetics). They were written by me using a combination of the textbook and class notes. I will also be uploading the other topics and creating bundles.
Topics Included:
- Exothermic and endothermic reactions
- Enthalpy
-...
Kinetics
5.1 Collision Theory
5.1 collision theory
- For a chemical reaction to occur the reactants have to collide
with sufficient energy and the correct orientation. 5.2 the maxwell-Boltzmann distribution
- Not all collisions will be successful, some will not have enough 5.3 catalysts
energy, and some will not have the correct orientation.
- The rate of reaction is the change in concentration of any of the reactants or products with unit
time.
Factors affecting the rate of chemical reactions:
- Increasing the temperature
o A higher temperature means that the particles have a higher kinetic energy.
o This means they will collide more frequently, and a greater proportion of collisions will have a
high enough energy to react.
- Increasing concentration of a solution/ pressure of a gas
o A higher concentration means that there are more reactants per unit volume and therefore
more frequent collisions.
- Increased surface area of solids
o A higher surface area means that there are more particles for collision on the
surface and therefore more frequent collisions.
- Catalysts
o Changes the rate of a reaction without being used.
o Provides an alternative pathway with a lower activation energy.
- The activation energy is the minimum energy needed to start a reaction.
- The species at the top of the curve on an enthalpy diagram is called the transition
state.
5.2 The Maxwell-Boltzmann Distribution
- The particles in any gas or solution are moving at different speeds. If you
plot a graph of energy against the number of particles that have that
energy, it forms a Maxwell-Boltzmann distribution.
Maxwell-Boltzmann distribution:
- Line goes through the origin
- The line approaches the x-axis but never touches it.
- The most probable energy is at the highest point of the curve.
- The average energy will not be the same as the most probable energy.
- No particles have zero energy.
The Effect of Temperature:
- The new curve will have a maximum that is lower in height but higher in energy.
- The curve is shifted to the right.
- The higher temperature line will only cross the lower line once.
- The total area under the curves is equal, as it represents the number of particles.
- At a higher temperature more of the molecules have an energy greater than Ea so a higher proportion
of collisions will result in a reaction.
5.3 Catalysts
- Catalysts are substances that affect the rate of chemical reactions without being chemically changed
themselves at the end of the reaction.
- Catalysts provide an alternate reaction pathway at a lower activation energy.
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