Measuring Rates of Reaction

Finding rate of reaction

• The rate of reaction can be found by measuring the amount of product formed in a certain period of time.

• The mass of a solid product is often measured in grams, while the volume of a gaseous product is often measured in cm3.

• The time period chosen may depend upon the rate of the reaction.

  • For example, it may be a few seconds for a fast reaction or a few minutes for a slow reaction.

• The units for rate of reaction are commonly written as:

  • g/s or g/min
  • cm3/s or cm3/min

• There are three main methods of measuring rate:

  • measuring the volume of gas given off by a reaction over time
  • measuring the loss of mass of a reaction over time when a gas is produced
  • measuring the amount of light that passes through a reaction mixture (as a precipitate forms) over time – this can be done by inspection or using a light sensor and data logger

Measuring the rate where a gas is produced

• The apparatus needed depends on the nature of the product being measured.

• Mass

• The mass of a substance – solid, liquid or gas – is measured with a balance.

  • This mass balance could be attached to a data logger to measure the decrease in mass against time continuously and produce a graph instantly.
  • The data logger does not make the mass balance any more accurate.
  • Cotton wool is used in the neck of the flask as it allows the gas to escape.

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