Rate of reaction
- Also called reaction rate, this is defined as the increase in molar concentration of product of a reaction per unit time, or can also be defined as the decrease in molar concentration of reactant per unit time.
- Do take note that as a reaction occurs, the concentration of reactants decreases, while the concentration of products increases.
- The rate of reaction is calculated by the change of the concentration of product or reactant per unit time.
- The rate of reaction should be fastest at the start of the reaction, slowing down as the reaction progresses, and slows down to a stop once the reaction is over when all the reactants are used up.

Collision theory
- This theory states that a chemical reaction takes place when particles of the reactants collide with sufficient kinetic energy to initiate the reaction. This sufficient energy to react is also known as the activation energy E_a.
Factors affecting the rate of reaction
- Concentration of reactants:
  - A higher concentration of reactants means there are more collisions between the particles, leading to a higher reaction rate
  - A lower concentration of reactants means less collisions between the particles, leading to a lower reaction rate.
- Pressure of gaseous reactants:
  - A higher pressure means a higher concentration of gas molecules in a smaller volume, resulting in more collisions between reactant particles and a higher reaction rate.
  - On the other hand, a lower pressure means a lower concentration of gas in a larger volume, resulting in less collisions and lower reaction rate.
- Temperature of reactants:
  - The activation energy E_a is the minimum kinetic energy a particle must have for a reaction to occur.
  - A higher temperature means more particles have higher kinetic energy than the activation energy required for the reaction to proceed, which results in a higher rate of reaction. The reaction also proceeds faster and completes in a shorter amount of time.
  - On the other hand, a lower temperature means less particles have higher kinetic energy than the activation energy required for the reaction to proceed, resulting in a lower rate of reaction.
- Surface area of reactants (size):
  - The smaller the particle size, the larger the surface area, which results in a higher number of collisions that can occur at any time, which leads to faster reaction rates.
  - To demonstrate how smaller particle sizes have higher surface area, we can demonstrate using this example: the larger cube and the 8 smaller cubes have the same volume, but the 8 cubes have twice the surface area compared to the 1 large cube.
- Using a catalyst
  - A catalyst is a substance that speeds up a chemical reaction and remains unchanged at the endof the reaction. The catalyst provides a different reaction pathway which decreases the activation energy E_a to start the reaction.
  - A reaction using a catalyst would have a higher rate of reaction, because more particles have sufficient energy (due to the lowered activation energy) to react.
  - On the other hand, a reaction without a catalyst would have a lower rate of reaction, as less particles have enough energy to react due to the higher activation energy.

6.02 - Reaction Rate

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