Specific heat and heat capacity explain how much energy is needed to warm a substance. They matter in chemistry because temperature changes reveal how energy moves during heating, cooling, dissolving, and reactions. Water is especially important because it can absorb a large amount of heat while changing temperature only slowly.
This helps regulate climate, living organisms, and many laboratory processes.
Heat, symbol q, is energy transferred because of a temperature difference, while temperature measures the average kinetic energy of particles. The basic calculation is q = mcΔT, where m is mass, c is specific heat, and ΔT is the change in temperature. Water has a high specific heat because hydrogen bonding between water molecules absorbs energy before molecular motion increases much.
In calorimetry, measuring a temperature change lets scientists calculate heat gained or lost by a substance.
Key Facts
- Heat is energy transferred because of a temperature difference, and its symbol is q.
- Temperature change is ΔT = Tfinal - Tinitial.
- Specific heat is the heat needed to raise 1 g of a substance by 1 °C.
- Heat calculation: q = mcΔT.
- Heat capacity is the heat needed to raise an entire object or sample by 1 °C, so C = q/ΔT.
- For liquid water, c = 4.184 J/g°C, which is high compared with many common substances.
Vocabulary
- Heat
- Heat is energy transferred from one object or substance to another because of a temperature difference.
- Specific heat
- Specific heat is the amount of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius.
- Heat capacity
- Heat capacity is the amount of heat required to raise the temperature of an entire sample or object by 1 degree Celsius.
- Temperature change
- Temperature change is the final temperature minus the initial temperature, written as ΔT = Tfinal - Tinitial.
- Calorimetry
- Calorimetry is the experimental measurement of heat transfer using observed temperature changes.
Common Mistakes to Avoid
- Using the wrong sign for ΔT: ΔT must be Tfinal - Tinitial, so heating gives a positive value and cooling gives a negative value.
- Confusing specific heat with heat capacity: specific heat depends on the material per gram, while heat capacity depends on the entire amount of material present.
- Forgetting units in q = mcΔT: mass, specific heat, and temperature change must use compatible units such as g, J/g°C, and °C.
- Assuming a large temperature change always means a large heat transfer: heat also depends on mass and specific heat, so a small sample may require little energy.
Practice Questions
- 1 A 250.0 g sample of water is heated from 20.0 °C to 35.0 °C. Using c = 4.184 J/g°C, calculate q in joules.
- 2 A 50.0 g piece of copper absorbs 385 J of heat and warms from 25.0 °C to 45.0 °C. Calculate the specific heat of copper.
- 3 Two equal masses of water and iron receive the same amount of heat. Explain which substance will have the smaller temperature change and why.