Heat Capacity Calculator
Heat (J)
41860
How it works
Heat capacity describes how much thermal energy a substance can store. Specific heat capacity (c) is the energy required to raise 1 kg of substance by 1°C: Q = m × c × ΔT. Molar heat capacity is defined per mole of substance.
**Specific heat values** Water: 4186 J/(kg·K) — exceptionally high, making water excellent for thermal storage and coolant. Ice: 2090 J/(kg·K). Steel: 490–500 J/(kg·K). Aluminum: 900 J/(kg·K). Air: 1005 J/(kg·K) (constant pressure). Concrete: 880 J/(kg·K). The high specific heat of water explains ocean thermal inertia and climate moderation in coastal regions.
**Latent heat** Phase changes require energy without temperature change: latent heat of fusion (melting/freezing) and latent heat of vaporization (boiling/condensation). Water: heat of fusion = 334 kJ/kg, heat of vaporization = 2260 kJ/kg. Evaporating 1 kg of water requires the same energy as heating 540 kg of water by 1°C — this is why sweating is an efficient cooling mechanism and why steam has enormous energy content.
**Thermal mass in building design** High thermal mass (concrete, brick, stone) moderates temperature swings — absorbs heat during the day, releases it at night. This reduces peak cooling loads and can shift demand to off-peak hours. Passive solar design uses thermal mass walls to store solar gain and release it overnight.
**Calorimetry calculations** Heat lost by hot object = heat gained by cold object in a calorimeter (assuming no losses): m_hot × c_hot × (T_initial,hot - T_final) = m_cold × c_cold × (T_final - T_initial,cold). This allows measurement of unknown specific heats by observing equilibrium temperature.
Frequently Asked Questions
- Q = m × c × ΔT. Room dimensions: 5m × 4m × 2.5m = 50 m³. Air density ≈ 1.2 kg/m³, c_air = 1005 J/(kg·K). Mass of air = 50 × 1.2 = 60 kg. To heat from 10°C to 20°C: Q = 60 × 1005 × 10 = 603,000 J = 603 kJ ≈ 0.17 kWh. A 1 kW heater heats this air in ~10 minutes. However, real rooms lose heat continuously through walls, windows, and infiltration — the heater must match steady-state heat loss, not just initial warm-up energy.
- Water's specific heat (4186 J/kg·K) is 4–9× higher than most other liquids: ethanol 2440, hydraulic oil 1800, engine oil 1900, glycol 2400. This means water absorbs more heat per kilogram per degree rise — you need less of it to carry the same heat load. Water also has excellent thermal conductivity (0.6 W/m·K vs. oil 0.15 W/m·K) and is cheap and non-toxic. Limitations: freezing point (antifreeze additives required), boiling point (pressure cooling systems or glycol mixtures), and corrosiveness (inhibitors required).
- High thermal mass materials (concrete 880 J/kg·K, brick 840 J/kg·K, water 4186 J/kg·K) store solar energy and release it slowly, reducing temperature swings. A 200 mm concrete floor in a 50 m² room: mass = 50 × 0.2 × 2300 kg/m³ = 23,000 kg. To absorb 5°C of daytime solar gain: Q = 23,000 × 880 × 5 = 101 MJ = 28 kWh. This same energy releases overnight, maintaining comfortable temperatures. Poorly insulated lightweight buildings (low thermal mass) overheat rapidly in sun and cool quickly at night.
- Cp (constant pressure): heat added at constant pressure — some energy goes into work of expansion (PΔV), rest raises temperature. Cv (constant volume): all heat goes into raising temperature. For solids and liquids, the difference is negligible (Cp ≈ Cv) because they expand very little. For gases, the difference is significant: Cp = Cv + R (R = 8.314 J/mol·K for ideal gas). For air: Cv = 717 J/kg·K, Cp = 1005 J/kg·K. The ratio γ = Cp/Cv = 1.4 for diatomic gases — determines speed of sound, adiabatic compression temperature rise, and isentropic efficiency of compressors and turbines.