Specific Heat Capacity

• Specific Heat Capacity describes the energy required to raise the temperature of a substance:

  • The 'specific' part refers to raising the temperature of specifically 1 kg of a substance by 1 degree
• • Changes to the internal energy of a substance is usually due to transfer of thermal energy 
  • The amount of thermal energy transferred ΔQ is related to the change in temperature Δθ by the equation
• Change in thermal energy  = Mass × Specific heat capacity  × Change in temperature

  ΔQ = mcΔθ
• Where:

  • ΔQ = change in thermal energy, in joules (J)
  • m = mass, in kilograms (kg)
  • c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C)
  • Δθ = change in temperature, in degrees Celsius (°C)
• Investigating Specific Heat Capacity, Equipment List:

  
• Experiment 1: Determining the Specific Heat Capacity of Water

  Aim of the Experiment

  • The aim of this experiment is to determine the specific heat capacity of water by measuring the energy required to increase the temperature of a known amount by 1°C.
• Experiment 1: Determining the Specific Heat Capacity of Water. Method:

  1. Place the beaker on the digital balance and press 'tare'
  2. Add approximately 250 ml of water and record the mass of the water
  3. Place the immersion heater and thermometer in the water
  4. Connect up the circuit as shown in the diagram, with the ammeter in series with the power supply and immersion heater, and the voltmeter in parallel with immersion heater
• Experiment 1: Determining the Specific Heat Capacity of Water. Method: (part 2)

  1. Record the initial temperature of the water at time 0 s
  2. Turn on the power supply, set at approximately 10 V, and start the stopwatch
  3. Record the voltage and current
  4. Continue to record the temperature, voltage and current every 60 seconds for 10 minutes
• Analysis of Results:

  • Calculate the energy supplied each minute using the formula:Electrical energy (J) = voltage (V) × current (A) × time (s)
• The gradient of the graph is equal to the specific heat capacity of the water, assuming a perfectly efficient immersion heater:

  
• Experiment 2: Obtaining a Temperature-Time Graph for Melting Ice

  Aim of the Experiment:

  • The aim of this experiment is to plot a graph of the temperature of ice, against time, as it is heated to water
• Experiment 2: Obtaining a Temperature-Time Graph for Melting Ice. Method:

  1. Place some ice in a beaker so it is about half-full
  2. Place a thermometer in the beaker
  3. Place the beaker on a tripod and gauze and slowly start to heat it using a bunsen burner
  4. As the beaker is heated, take regular temperature measurements (e.g. at one minute intervals)
  5. Continue this whilst the substance changes state (from solid to liquid)
  6. The results can then be plotted on a graph
• A heating curve will show a flat section whilst the ice is melting:

  
• Systematic Errors:

  • Ensure the digital balance is set to zero before taking measurements of mass
  • It may be necessary to determine the efficiency of the immersion heater before experiment 1:
  • The specific heat capacity of water has a known value of 4200 J/kg/°C
  • If the efficiency of the heater is less than 1 then the values obtained for specific heat capacity will be larger than expected
• Random Errors:

  • Stir the ice water constantly whilst heating in experiment 2
  • When the current or voltage values appear to be changing between two values next to one another then be consistent in choosing the higher value
• Equipment List: