Chemistry - Speed of reaction


Speed of reaction:

 The speed of reaction can be measured by two methods:
1. mass loss in a reacting flask per unit time.
2. product formation per unit time.

The gradient of the graph indicates the speed of the reaction.
The greater the gradient, the faster the reaction.

The mass loss of reacting flask = the mass of gas released.

Rate of mass loss: (Mass time graph) 

Cotton wool in an apparatus is to prevent any liquid from escaping from the flask,
so that the mass loss is due to gas escape only.

 Rate of product formation: (Gas time graph)
- When a reaction produces a gas, it can be collected using a syringe.
- The speed of reaction can be measured by the volume of gas produced per unit time.

When the gradient is zero, it means the reaction has stopped.

The collision theory:

- Reacting particles must collide with each other so that a chemical reaction can take place.
- But they must have a minimum amount of activation energy before a reaction can occur.
- These colliding particles with less than activation energy will just bounce off from each other.
- This shows that the collision of the reacting particles must achieve the minimum activation energy to break their original chemical bonds in order to form new bonds in the product.

Factors affecting the speed of reaction:
1. Concentration of the reacting solution.
2. Pressure of gaseous reactants
3. Particle size of solid reactants
4. Temperature of the reacting system
5. Catalyst.

Above 5 changes the 1. number of collisions per unit time,  2. the collision energy.

If the frequency of collisions increases, the chance for effective collisions increases. Therefore, the speed of reaction increases.

1. Concentration of the reacting solution:

  • Increasing the concentration of a reacting solution means increasing the number of reactants in the same volume.
  • The number of collisions between the reactants increases per unit time,
    so the chance for effective collisions increases, which speeds up the speed of reaction.

Thus, when the concentration of any reactant in a solution increases, the speed of reaction increases too. 

Take note : for the graph, mass loss is the same but the time end quicker.  



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