Specific Heat (chemistry)
Specific heat capacity (c) is the amount of heat energy required to raise the temperature of one gram of a substance by one degree Celsius (or one Kelvin). It is an intrinsic physical property of a material that reflects how resistant a substance is to temperature change, with water having the exceptionally high value of 4.184 J/(g·°C). Specific heat is fundamental to calorimetry calculations and explains phenomena such as coastal climate moderation due to the ocean's high heat capacity.
Key Formula
c = q / (m × ΔT)
LaTeX: c = \frac{q}{m \, \Delta T}
| Symbol | Meaning | Unit |
|---|---|---|
| c | Specific heat capacity | J/(g·°C) |
| q | Heat transferred | J |
| m | Mass of substance | g |
| ΔT | Temperature change | °C or K |
Worked Example
Problem
A 50.0 g block of iron at 100.0 °C is dropped into 200.0 g of water at 20.0 °C. What is the final equilibrium temperature? Specific heat of iron = 0.449 J/(g·°C), specific heat of water = 4.184 J/(g·°C).
Solution
Step 1: Use heat balance: q_iron + q_water = 0 (no heat lost to surroundings). Step 2: m_Fe × c_Fe × (T_f − 100) + m_w × c_w × (T_f − 20) = 0. 50.0 × 0.449 × (T_f − 100) + 200.0 × 4.184 × (T_f − 20) = 0 Step 3: Expand: 22.45(T_f − 100) + 836.8(T_f − 20) = 0. 22.45·T_f − 2245 + 836.8·T_f − 16736 = 0 Step 4: 859.25·T_f = 18981 Step 5: T_f = 18981 / 859.25 = 22.09 °C.
Answer
T_final ≈ 22.1 °C
Specific Heat Capacities of Common Substances
| Substance | State | Specific Heat c (J/g·°C) | Relative Heat Capacity |
|---|---|---|---|
| Water | Liquid | 4.184 | Very high (reference) |
| Ice | Solid | 2.093 | Moderate |
| Steam | Gas | 2.010 | Moderate |
| Aluminum | Solid | 0.897 | Low |
| Iron | Solid | 0.449 | Very low |
| Copper | Solid | 0.385 | Very low |
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Related Terms
Calorimetry
Calorimetry is the experimental science of measuring the heat exchanged during chemical reactions, physical changes, or heat capacity determinations using an instrument called a calorimeter. The fundamental principle is conservation of energy: heat released by the reaction equals heat absorbed by the calorimeter and its contents. Two main types are constant-pressure calorimetry (coffee-cup calorimeter) and constant-volume calorimetry (bomb calorimeter), each suited to different experimental conditions.
Standard Enthalpy
Standard enthalpy refers to the enthalpy change of a process measured under standard conditions: 298.15 K (25 °C) and 1 bar (approximately 1 atm) pressure, with all substances in their standard states. Standard enthalpy values provide a universal reference for comparing thermochemical data across different reactions and sources. The symbol ΔH° (read "delta H naught" or "delta H standard") denotes a standard enthalpy change.
Phase Diagram
A phase diagram is a graphical representation showing the equilibrium states of matter (solid, liquid, gas, and sometimes plasma or supercritical fluid) for a given substance as a function of temperature and pressure. The diagram delineates phase boundaries (lines along which two phases coexist), the triple point (where all three phases coexist), and the critical point (beyond which liquid and gas phases become indistinguishable). Phase diagrams are essential tools in materials science, chemical engineering, and geochemistry for predicting phase behavior under varying conditions.
From Latin 'specificus' (particular to a species) and Old English 'haetu' (heat). The concept of specific heat was first quantified by Scottish chemist Joseph Black in the 1760s during his study of calorimetry and latent heat.