Berry Berry Easy wishes to present all Form 5 SPM Chemistry student with some Berry Essence notes (only the most important concepts are given here) which all students should understand before they can declare themselves as understanding the topic of “Rate of Reaction”.
Try to learn by visualising (using a 3D object inside your head) the effects of the different factors on reaction rates. By visualising it in 3D inside your head, you don’t have to memorise anything, it will come naturally in exams when you need to write all the factors affecting reaction rates. Try also to visual two molecules colliding into each other to grasp the concept of collisions. Visualising is the key to understanding this topic, rather than plain memorisation.
SPM Form 5 – Terminology and Concepts: Rate of Reaction
Chemical reaction can be observed by
- Volume of gas liberated (Laboratory Work 1.2, Experiment 1.1)
- Pressure changes
- Precipitate formation (Experiment 1.2)
- Change in the concentration of a liquid reactant
- Change in the pH value
- Change in mass during the reaction
- Colour changes / Change on the colour of intensity
- Temperature changes (Experiment 1.3)
Rate of reaction is the measurement of the speed which reactants are converted into products in a chemical reaction.
Average rate of reaction is the average value of the rate of reaction over an interval of time.
Instantaneous rate of reaction / Rate of reaction at a given time are the actual rate of reaction at that instant.
Factors Affecting the Rate of Reaction
- Total surface area of solid reactant
- Concentration of reactant
- Temperature of reactant
- Use of catalyst
- Pressure of gaseous reactant
Effect of total surface area of solid reactant on the rate of reaction
- Smaller the size (increase the total surface area), cm3, of the solid reactant, the higher the rate of reaction, cm3 s-1 or cm3 min-1.
Effect of concentration of a liquid reactant on the rate of reaction
- Higher the concentration, mol dm-3, of a liquid reactant, the higher the rate of reaction, mol dm-3 s-1 or mol dm-3 min-1.
Effect of temperature on the rate of reaction
- Increase in temperature, the higher the rate of reaction.
Effect of catalyst on the rate of reaction
- Alters the rate of reaction
- It is specific in its action. It can only catalyse a particular reaction
- Does not change the quantity of products formed
- Only small amount of catalyst is needed to increases the rate of reaction. (An increase in the quantity of catalyst will increase the rate of reaction but only a very slight increase.)
- Catalyst remains chemically unchanged but may undergo physical changes.
Effect of pressure on the rate of reaction
- Increase in pressure, the higher the rate of reaction (reversible reaction and gaseous reactants and gaseous product).
Collision Theory and Activation Energy
Collision theory states a reaction occur when the particle of the reactant collide with each other with the correct orientation and achieve activation energy.
Effective collision is the particles collide with the correct orientation and achieve activation energy which result in a reaction.
Ineffective collision is the particles that collide with energy less than activation energy or wrong orientation.
Activation energy, Ea, is the minimum kinetic energy that colliding particles of the reactants must possess. It can be visualised by energy profile diagram.
Keywords: frequency of the collision; frequency of effective collision, rate of reaction
Common Mistakes (SPM Form 5 – Rate of Reaction)
- Never use word: ‘faster the rate of reaction’ or ‘ slower the rate of reaction’. (use word such as ‘ increases’, ‘decreases’, ‘ higher’ or ‘lower’.
- Average rate of reaction is berry different from instantaneous rate of reaction. (Instantaneous can be determined by drawing a tangent on the graph’s curve).
- Time reading: 1 decimal point. (It also depends on the measurement apparatus either a normal stopwatch or digital stopwatch) Example: 21.0 seconds and 45.5 seconds.
- Measuring cylinder reading: 1 decimal point. Example: 5.0 cm3 and 4.5 cm3.
- Burette reading: 2 decimal points. Example: 50.00 cm3 and 45.25 cm3.
- Pipette reading: 1 decimal point: Example: 25.0 cm3 and 10.0 cm3.
Important Tips – SPM – Rate of Reaction
Rate of Reaction will be Berry Important Topic (BIT) for the Paper 2 (essay) and Paper 3 that young berries could not skip as one of your revision routine. Do take notes on the graphs and these few experiments that listed below.
Experiment 1.1 Effect of surface area on the rate of reaction.
Experiment 1.2 Effect of concentration on the rate of reaction.
Experiment 1.3 Effect of temperature on the rate of reaction.
Experiment 1.5: Effect of the amount of catalyst on the rate of reaction.
Activity: Factors affecting the rate of reaction.