Energy changes in systems: Required practical activity 14: an investigation to determine the specific heat capacity of one or more materials. The investigation will involve linking the decrease of one energy store (or work done) to the increase in temperature and subsequent increase in thermal energy stored.

The idea

This required practical measures how much energy is transferred to a material and the resulting temperature rise, then uses ΔE = mcΔθ to find specific heat capacity. A typical method uses a heater or falling mass to transfer energy to a metal block or water. Measure the mass, record the initial temperature, transfer a known amount of energy, stir, and record the highest steady temperature. The energy supplied may come from electrical work, calculated as power × time, or from gravitational potential energy lost by a falling mass, calculated as mgh. The decrease in one energy store equals the increase in thermal energy stored, assuming no unwanted transfer to the surroundings. Plot or compare energy transferred against temperature rise; the gradient, combined with mass, gives specific heat capacity.

What earns the marks

• Measure the mass of the material accurately using a balance and record it in kilograms.
• Record the initial temperature and the final steady temperature, then calculate the temperature change.
• Supply a measured amount of energy, for example using an electric heater with power × time or a falling mass with mgh.
• Link the energy transferred to the temperature rise using ΔE = mcΔθ and rearrange to find c.
• Identify and reduce unwanted energy transfers to the surroundings, such as insulating the container or using a lid.
• Repeat measurements and calculate a mean to improve reliability, and consider whether the material is one substance or a mixture.

Common mistakes and how to put them right

• Using the final temperature alone instead of the temperature change.

  Put it right: Subtract the initial temperature from the final temperature.

• Ignoring energy lost to the surroundings, which makes the calculated specific heat capacity too high or too low depending on the method.

  Put it right: Insulate and account for losses.

• Mixing units, such as using grams with J/kg°C or seconds with minutes.

  Put it right: Convert all values to kg, J, °C and s before calculating.

Exam tips

• Describe the method as a sequence: measure mass, record initial temperature, transfer energy, record final temperature, calculate.
• State the equation used to find energy supplied and show the rearrangement to c = ΔE / (mΔθ).
• Explain one improvement that reduces uncertainty, such as insulating the block or repeating and averaging readings.