Specific heat capacity: definition and practical
Principles of energy • Energy stores and changes
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Key concepts
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Definition and units
Specific heat capacity is the amount of energy required to raise the temperature of one kilogram of a substance by one degree Celsius. The SI units are joules per kilogram per degree Celsius (J/kg °C) . The definition applies only while the substance remains in the same state (no phase change) and over the measured temperature range.
Equation and calculation
The change in thermal energy (E) of a mass (m) caused by a temperature change (ΔT) relates to specific heat capacity (c) by the equation c = E ÷ (m × ΔT) . Rearrangement allows calculation of E or ΔT when c and the other variables are known. Accurate measurements of energy, mass and temperature change are necessary to obtain a reliable value of c.
Physical meaning and examples
A substance with a high specific heat capacity absorbs more energy for the same temperature rise than a substance with a low value. Water has a high specific heat capacity, so a given mass of water stores and releases large amounts of thermal energy for small temperature changes; this property influences heating systems and thermal stability of environments . Materials with low specific heat capacity heat and cool more rapidly under the same energy input.
Required practical: core idea
The practical transfers electrical energy from an immersion heater to a material sample and measures the energy supplied with a joulemeter while recording the sample mass and temperature change. The decrease in the electrical energy store causes an increase in the thermal energy store of the sample; measuring both sides of that energy transfer allows calculation of c . The method assumes negligible energy losses to the surroundings or applies corrections for measured losses.
Step-by-step practical method
Measure the mass of the sample in kilograms. Place an immersion heater and a thermometer into the sample so both contact the material. Connect the heater to a power supply and a joulemeter; record the initial joulemeter reading and the initial temperature. Switch on the heater for a measured time, stirring the sample if liquid, then record the final joulemeter reading and final temperature. Calculate the energy supplied from the joulemeter and use c = E ÷ (m × ΔT) to find the specific heat capacity .
Sources of error and improvements
Heat loss to the surroundings causes the measured energy supplied to be larger than the energy gained by the sample, producing an overestimate of c; insulating the sample and adding a lid reduces this error . Inaccurate temperature readings occur if the thermometer or sensor is not near the heated region; placing the thermometer close to the heater and stirring liquids promotes uniform temperature. Calibration errors for the joulemeter or power supply produce systematic error; verifying instrument accuracy and repeating measurements improves reliability.
Key notes
Important points to keep in mind