Reactions

Rate of Reaction

The rate of reaction is the speed of a chemical reaction. It is how quickly reactant particles are converted into product particles.

Measuring Rate of Reaction

Some reactions produce a gas. There are a few ways to measure the rate of reaction in this situation. It is possible:

  • collect the gas in a syringe and record its volume over fixed time intervals
  • calculate the mass lost as gas over fixed time intervals

Usually, it is easier to record the volume of gas instead of the mass lost.

Interpreting Data

Graphs are used to visualise the rate of reaction. The slope or steepness of the graphed curve represents the rate of reaction.

The graph of a typical reaction with amount of reactants plotted against time would look like an exponentially decreasing curve. This is because the rate of reaction decreases as the amount of reactants decreases. The opposite of this graph would be amount of products against time.

Factors Affecting Rate of Reaction

All of these factors increase the rate of reaction.

Concentration

  • More reactant particles exist per unit volume
  • More collisions occur per second

Temperature

  • Particles have more kinetic energy
  • Particles collide with more force
  • More particles have enough activation energy to react
  • More successful collisions occur per second

Surface Area

  • More reactant particles are exposed to each other
  • More collisions occur per second
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It is good to finish explanations by stating whether the rate of reaction increases or not.

Dangers

Increasing the rate of reaction can create a danger of explosive combustion with fine powders and gases.

Redox

A redox reaction involves both oxidation and reduction. Substitution reactions are a common example of redox reactions. A more reactive metal can react with an ionic compound and substitute itself for the less reactive metal. The more reactive metal loses electrons while the less reactive metal gains electrons.

Mg + CuSO4 → Cu + MgSO4
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OILRIG is a good acronym which stands for oxidation is loss (of electrons) and reduction is gain (of electrons).

Reduction

Reduction can be described as the loss of oxygen or the gain of electrons.

Cu2+ + 2e- → Cu

A reducing agent is a chemical that reduces another reactant. This means reducing agents lose electrons.

Oxidation

Oxidation can be describes as the gain of oxygen or the loss of electrons.

Mg - 2e- → Mg2+

A oxidising agent is a chemical that oxidises another reactant. This means reducing agents gain electrons.