Rate of the reaction= amount of substance formed or used/ time
For the calculation of Rate of reaction, amount of a product produced over time can be measured with time. e.g : measuring the volume of hydrogen gas produced from a acid and a metal reaction with time
or a measurement of reduction of mass over time. e.g: reduction of mass of due to escaping of the carbon dioxide gas from a reaction between an acid and a metal carbonate.
Whatever the method used to measure the rate, it should be an indicator of the reaction progress.
Rate of the reaction depends on several factors.
Factors affecting rate of reaction:
- concentration
- pressure
- particle size
- temperature
Effect of these factors can be tested in a laboratory too.
1. Effect of Concentration
Lets suppose two students performed an experiment to measure rate of reaction
Student 1 Student 2
Mg 2g ribbon Mg 2g ribbon
HCl 0.1 mol/dm3 concentration HCl 2 mol/dm3 concentration
20 ml HCl 20 ml HCl
If these experiments were conducted under same temperature. Student 2 can expect the highest reaction rate.
The reason for this can be explained by the collisions between the particles.
For a reaction to happen reactant particles should collide with each other. these collisions will be more often When the concentration is high as these will be more reactant particles per unit volume for the reaction.
Experimental setup for the reaction will be as follows.
If the reading was measured, the graph obtained will be as follows. The rate is high in the begining and rate slows as the reactants are used up. When the limited reactant is over, the reaction stops.
If the results of both the experiment one and two is drawn on the same graph, it would look like following. Reaction speed is high for the experiment with the highest HCl concentration. However the total volume produced after the reactions are over will be the same as both the experiments have used the same mass of Mg and HCl is in excess.
2. Effect of Pressure
Effect of pressure is applicable for gaseous reactants only. If two reactions were performed as follows , which experiment will show the highest reaction rate?
Experiment 1 Experiment 2
CO 20 cm3 CO 20 cm3
O2 20 cm3 O2 20 cm3
Pressure 1 atm Pressure 2 atm
if the volume and temperature is same experiment 2 will have the highest reaction rate as the particles collisions are more likely under the high pressure system.
3. Effect of particle size
Would it be easy to dissolve granulated sugar in water or powdered sugar? Powdered sugar is easily soluble than granulated sugar. The reason for this is more surface area is available in powdered sugar. Rate of reaction is also affected by particle size due to the same reason.
Compare the following two experiments
Experiment 1 Experiment 2
Zn 2g powdered Zn 2g granulated
HCl 2M 20 ml HCl 2M 20 ml
If these experiments were performed under same temperature, Experiment 1 will have the highest reaction rate because more surface area is available for the particles to collide more often.
4. Effect of temperature
It is easy to dissolve sugar in a hot cup of tea than in a cold drink. Reaction rates are also affected by the temperature.
If two experiments using same amount of same kind of reactants and one was done under a high temperature, that experiment will show a higher rate in the reaction. Reason for this is, when the temperature is high reactant particles have more kinetic energy them which makes the collisions between them more faster, making the rate of the reaction high.
Next about redox reactions
11:54 PM
concentration. graph
Effect of pressure
effect of temperature
factors affecting rate of reaction
measuring rate of reaction
particle size
Rate of reaction
