Rate of Reaction

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Here are the main factors that affect the rate of reaction:

Temperature: The higher the temperature, the more will particles move and the faster will be the reaction. This is because all the heat energy given to reactants turn to kinetic energy in them; the more the kinetic energy, the more the chances of collision with other molecules. It is useful to know here that all reactions need to have some energy to initiate, this is called activation energy. So, there are some reactions which won’t even begin until temperature is increased adequately.

Surface Area: A block or a lump will react very slowly as compared to the powdered form of the same substance. This is because powder has more surface area as compared to a lump. And the more the area, the more quickly will they be able to interact. If you heat a marble piece, it will take a long while to convert it into calcium oxide. It is because the core of the marble piece won’t get enough heat. On the other hand, powdered marble will decompose very quickly.

Catalyst: A catalyst is a substance that alters the rate of reaction, but doesn’t undergo a chemical change. A catalyst can either speed up, or slow the reaction, as desired. A good example is the making of oxygen at laboratory scale. It is done by decomposing Potassium chlorate. Heating Potassium Chlorate without catalyst is a very slow process. The reaction might take a full hour before it completes. Having manganese dioxide as a catalyst can increase the rate of reaction, and complete it within the matter of minutes. Enzymes are biological catalysts. Some reactions require enzymes to begin. Enzymes are generally obtained from microorganisms. Yeast or Saccharomyces Cerevisiae is used to convert sugar to ethanol.

Concentration:  The rate of reactions which happen in solutions, depend on concentration. Concentration is moles of a substance per unit volume. The greater the concentration the faster will be the reaction. This is especially true for reactions in Chemical Equilibrium. The law of Mass Actions states that “Rate of reaction is directly proportional to active masses of substances”. Here active masses meaning concentration.

Light: The rate of some chemical reactions depends on the presence of light. Silver salts are specially sensitive to light, that’s why they are used in photography. Plants rely on light to do photosynthesis, which converts carbon-dioxide to oxygen. Such reactions are called photochemical reactions.

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