Chemistry · Thermodynamics · NEET
Heat capacity is the heat you must supply to a body to make its temperature go up by 1 kelvin (which is the same as 1 °C). If you give heat q and the temperature rises by ΔT, then C = q/ΔT. So C tells you how much heat 'one degree of warming' costs for that particular object. A large pot of water has a high heat capacity because it needs a lot of heat to warm up; a small nail has a low heat capacity.
The formula is q = C·ΔT, which rearranges to C = q/ΔT. Here q is the heat added (in joules, J) and ΔT is the temperature change (in kelvin, K). So the unit of C is joule per kelvin (J K⁻¹ or J/K). Because 1 K and 1 °C are the same size of step, you can also write it as J °C⁻¹. NEET numerical questions expect answers in J/K.
No, and this is the most common mix-up. Heat capacity (C) is for the WHOLE object — it depends on how much material is present. Specific heat capacity (small c) is per unit MASS, so its formula is q = m·c·ΔT and its unit is J kg⁻¹ K⁻¹ (or J g⁻¹ K⁻¹). The link is C = m·c: multiply specific heat by the mass to get the total heat capacity. Molar heat capacity is a third version — per mole instead of per gram.
C is the heat capacity, NOT the heat. The heat is q. Read the equation as: heat supplied (q) equals heat capacity (C) times temperature change (ΔT). Students often see 'C' and think 'calorie' or 'heat' — but here C is a property of the object that tells you how resistant it is to temperature change. A big C means the temperature rises only a little for a given amount of heat.
Because its value depends on the AMOUNT of substance present. If you double the mass of water, you need double the heat to raise its temperature by 1 K, so the heat capacity doubles. Any property that scales with the amount of matter (mass, volume, enthalpy, heat capacity) is called extensive. This is why we often prefer molar heat capacity (Cm) or specific heat (c), which are intensive and do not depend on how much you have.
Yes. The same substance has a slightly different heat capacity depending on the conditions. At constant volume it is called Cv, and at constant pressure it is called Cp. For gases Cp is larger than Cv because at constant pressure some heat also does work by expanding the gas. For NEET, remember the general definition C = q/ΔT first, then learn Cp and Cv as its two special cases.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the heat needed to raise an object's temperature by 1 kelvin: C = q/ΔT, with unit joule per kelvin (J/K).
Joule per kelvin (J K⁻¹), which is the same as J °C⁻¹ because 1 K and 1 °C are equal-sized steps.
Extensive — it depends on the amount of substance. Double the mass and the heat capacity doubles. Molar heat capacity and specific heat are the intensive versions.
C = m·c, where m is mass and c is specific heat capacity. Multiply the specific heat by the mass of the object to get its total heat capacity.
Cp is heat capacity at constant pressure and Cv is at constant volume. Both come from C = q/ΔT, just under different conditions; for gases Cp is larger than Cv.
