Higher Chemistry (rates of reaction)Watch
The rate of a reaction is usually thought of as the change in the concentration of products or reactants over time. In those reactions where the change in quantity is easily measured, the average rate of reaction can be calculated:
Average Rate is expressed in units such as g s-1, cm3 s-1 or mol l-1 s-1
However, it can be difficult to measure the product being produced or reactant used up – possibly because the reaction is very quick. The time taken for the reaction to complete can be used to calculate the relative rate of reaction. This is found by taking the reciprocal of the time to complete the reaction (1/t):
Relative rate of reaction is therefore expressed in units such as s-1 (per second).
Rates of chemical reactions can be controlled by chemists.
If reaction rates are too low, a manufacturing process will not be economically viable.
If reaction rates are too high, there is a risk of thermal explosion.
The rates of reactions are affected by changes in concentration, particle size and temperature, and collision theory can be used to explain these effects.
Graphs which use the same axes and place the results for different experiments in which the concentration or temperature are varied from one experiment to the next are common and show us how that variable affects the reaction progress.
Temperature is a measure of the average kinetic energy of the particles of a substance.
Activation energy is the minimum kinetic energy required by colliding particles before reaction can occur.
Energy distribution diagrams can be used to explain how an increase in temperature or, in some chemical reactions, the energy from light increases the number of particles with energy greater than the activation energy (Ea/EA).
Reactions increase their rate at higher temperatures because a higher proportion of the molecules involved have energy in excess of the activation energy so more successful collisions can occur.
A 10°C rise is responsible for an approximate doubling of rate in many reactions.
The effect of temperature on reaction rate can be explained in terms of an increase in the number of particles with energy greater than the activation energy.
Scholar is the best thing ever, i'm just putting up these summary notes incase anyone cannot access scholar. i hope this helps anyone in need of this
I've noticed a lot of people struggle with the topic of rates of reaction and particularly the underlying chemistry aspect of it so i'm posting notes i've taken on rates of reaction from last year to help anyone because i know i would've loved help like this last year.
Bringing intra and intermolecular bonds into things is a problem waiting to happen. What about, for example, HCl(aq) + NaOH(aq)?
Your essay doesn't really get across the importance of "frequency" too well, e.g. "The rate of the reaction will depend on the number of successful collisions taking place" (this needs something like "per second" adding) and "so they are more likely to collide more often" (you should avoid "more likely" type statements and just stick to something like "they collide more often").
The units of rate are not always s-1.
" In general, the higher the concentration of the reactant, the faster the rate of the reaction" - this is not true for zero order reactants.