Enzyme Investigation

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Back Ground Information

  • A rate is anything per unit time.
  • Things that speed up a reaction are things like the increase of (temperature, pressure, and concentration).
  • The unit for concentration is (Moles/dm3).
  • Powdered substances react quicker because the have wide surface area.
  • The rate of a chemical reaction i.e. how fast a reaction goes can be explained using the collision theory.

Collision Theory

In a chemical reaction: -

  1. Particles must collide
  2. The collision must have enough energy within it, for the particles to reach the transition state and form products.
  3. The particles must collide in the right orientation if products are to be formed.

           The more the number of collisions, the more the chance that the collisions will   have enough energy to reach the top of the activation energy to form products. In general most of the collisions either never have enough energy to form products or the particles do not collide in the right orientation, therefore only a few particles go on to form products (Maxwell Boltzmann Theory – A Levels!).

Factor that affects rates of reaction

Since the particles –molecules or ions- must collide to react. There are several factors that directly affects reaction rate:

  • Temperature: a rise in temperature greatly increases the rate of reaction. The average kinetic energy of the particles is increased; a higher proportion of them have an energy greater than the activation energy required for the reaction, and the number of effective collisions is higher. This means that there would be more collisions per unit time. Hence this increases the chances that more collisions will have enough energy to reach the transition state. In general a 10C increase in temperature will double the rate of reaction.

  • Concentration: This means the number of moles per unit volume (i.e. per dm3).

As we increase the concentration, we increase the number of particles per unit volume. The particles are now closer together, so there are more collisions per unit time. Hence increasing the chances that more collisions will reach the top of the activation energy to form products.

In General: Rate  concentration (As concentration doubles rate doubles).

  • Pressure: Increases in pressure increases the rate of reaction between gases because the molecules are brought closer together and collide more frequently. This is, in effect, an increase in concentration.
  • State of reactants: in reactions involving solids the rate of reaction is increased if the solid is finely divided, thus exposing a greater surface to attack. Fine iron powder will dissolved in cold dilute hydrochloric acid while coarse iron filing do not dissolved until the acid is heated.
  • Surface area:

The rate of reaction is greater in powdered Mg since it has a greater surface area. There are more collisions of the acid particles and the powdered Mg, and so the Mg will dissolve faster.

  • Enzymes:

Enzymes are biological catalyst, which are proteins in nature. Enzymes are specific they only break down one substance at a time. Once a substance locks into the active site of an enzyme, bonds form (temporarily) between enzymes & Substrate & the substrate is digested and released as products. This is called the lock and key mechanism.

Our body temperature is 37C, this provides an optimum temp. For enzymes in our body to work in. at lower temperatures the reaction slows down, where as at higher temperature the protein structure of the enzyme breaks down; the enzyme is DENATURED. Also enzymes have an optimum pH to work in.

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  • Catalyst: catalyst can dramatically increase the rate of a chemical reaction. They are defined as substances, which will alter the rate of a chemical reaction while remaining chemically unchanged at the end of the reaction. Only a small amount of a catalyst is required, and it can affect the rate of reaction for a long time. Catalysts are specifying in their action; a catalyst that increases the rate of one reaction may have no effect on another. The mechanism of catalyst is not totally understood, but there appear to be two main types. Some catalyst increases the rate ...

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