Rates of reaction

Reaction rate

The change in the amount of reactants or products per unit time (normally per second)

Continuous monitoring

The technique of measuring how the amount of a reactant or product changes over the complete course of the reaction

Examples of continuous monitoring techniques

• pH measurement

• Measuring gas volume

• Measuring loss of mass

• Colorimetry

• Titration

When can the rate of a reaction be followed using pH measurement

If one of the reactants or products is an acid or a base

What is used to measure the pH of a solution and how can the data collected be converted to concentration

• Using a pH probe

• [H⁺] = 10^-pH

When can the rate of reaction be followed by measuring gas volume or loss of mass

If a gas is given off

How can gas volumes be measured for following the rate of reaction

Using a gas syringe, record the volume of gas collected at regular time intervals

How can loss of mass be measured for following the rate of reaction

Using a balance, record the mass at regular time intervals

When can the rate of reaction be followed using colorimetry

If one of the products or reactants are coloured

Colorimeter

Can measure the absorbance of a solution, so the more concentrated the colour of the solution, the higher the absorbance

How can absorbance data be converted into concentrations

Calibration curve

How can the rate of reaction be followed using titration

Taking small samples of the reaction mixture at regular intervals, quenching them and titrating them using a suitable titrant

How can a reaction be quenched

Adding a chemical which stops the reaction, or decreasing the temperature a lot to significantly slow the reaction down.

How can the rate of reaction be calculated from a concentration-time graph

Calculating the gradient using a tangent

On a concentration-time graph, what does a gradient of 0 mean

The concentration no longer changes so the reaction has finished