Calorimetry and Change of State


  1. • Deals with measurement of heat.\\• Based on conservation of energy.\\• The bodies originally at higher temperature losses\\heat while the other body gains heat.\\i.e. Heat lost by one body = Heat gained by another body. This is known as the principle of calorimetry.\\• Quantity of heat is measured in Joule/calorie.\\

    • 1 Cal=4.2 Joule\\

  2. \textbf {Formula for Calorimetry:} \\Q=mc∆T\\Where,\\Q = heat evolved (heat absorbed − heat released) in joules (J)\\m = mass in kilograms (kg)\\c = specific heat capacity in J/k°C (or J/kg⋅K)\\∆T = temperature change in °C (or K)

Specific Heat Capacity

Specific heat capacity is defined as the amount of heat required to raise the\\temperature of 1 kilogram of a substance by 1 kelvin or 1 degree Celsius.\\CGS unit is calorie per gram per degree Celsius & SI unit it is Joule\\per kg per degree kelvin.\\S_{gas}>S_{liquid}>S_{solid}\\•Specific heat of water =4200 J/kgK or 1 Cal/gmK\\• Specific heat of ice= 2100J/KgK or 0.5 cal/gmK\\•Heavier the element smaller the specific heat(Sp. heat * At wt=6.4)

Thermal capacity

The thermal capacity of a body is the heat necessary to raise the\\temperature of the body by one degree.\\T.C=m.c, where m=mass, c=specific heat capacity. It’s unit is J/K or Cal/C.

Water Equivalent:
A substance's water equivalent is equivalent to the amount\\of water that is required to consume the same quantity of heat as that substance\\does for a temperature rise of one degree.\\Water equivalent of body = mass of body x specific heat capacity.\\Dimensionally it is equal to thermal capacity

Molar Heat Capacities

  1. \textbf{Amount of heat per mole necessary to increase the unit temperature. In the case of gas, heat lost or gained by body is given by\$

    At Constant Volume\\Q = n Cv ∆T\\

    At Constant Pressure\\Q = n Cp ∆T\\• \gamma = \dfrac[𝐶_𝑝}{𝐶_𝑣}\$

    • 𝐶𝑝 -𝐶𝑣=R (Mayer’s relation)\\

    • \gamma is 1.67 for monoatomic gases, 1.4 for diatomic gases, and 1.33 for\\polyatomic gases.

Latent heat

  1. •Heat required for changing state of substance without changing in temperature.\\• Isothermal Process.\\•No change in state.\\•Q=mL.\\

  2. \textbf {Latent heat of fusion:} \\•From solid to liquid.\\• For ice it is 80cal/g.\\

  3. \textbf {Latent heat of vaporization:} \\•From liquid to gas.\\•For boiling water it is 540cal/g.\\

  4. \textbf {Effect of pressure on melting of solid:} \\Melting point increases with increase in pressure for substances like Sulfur,\\Glass, Ghee, wax. (Expands on melting).\\Melting point decreases with increase in pressure for substance like Ice, Rubber.\\(Contracts on melting).\\Effect of Pressure on boiling point of liquid.\\With increase in pressure boiling point of all increases.


  1. A branch of physics that deals with the measurement of humidity especially of\\the atmosphere.\\The maximum limit of water vapor that a given quantity of air can hold at a particular temperature\\is termed as saturated vapor.\\In such a case, relative humidity will be 100 percent.\\For all other cases, where maximum limit of vapour is not reached, the vapor\\thus formed is termed as unsaturated vapor.\\

  2. \textbf {Triple Point:} \\In chemistry and physics, the triple point is the temperature and pressure at\\which solid, liquid, and vapor phases of a particular substance coexist in\\equilibrium. It is a specific case of thermodynamic phase equilibrium.\\The triple point for water is at 0.01 degree Celsius at 4.56 mm Hg and constant.

  3. \textbf {Dew Point:} \\Temperature at which vapor actually present in atm is sufficient to saturate it.\\

  4. \textbf {Absolute Humidity:} \\Amount of water vapor actually present in the unit volume is called Absolute humidity.\\

  5. \textbf {Relative Humidity:} \\The amount of water vapor present in air expressed as a percentage of the\\amount needed for saturation at the same temperature.\\R.H= \frac{m}{M} *100% Also R.H= \frac{p}{P}*100%; Where p=SVP at dew point and P=svp at room temperature\\(SVP is saturated vapor pressure)

Read and Digest

  1. SVP(Saturated Vapour Pressure) < UVP(Unsaturated vapor Pressure) [Always]\\

  2. Specific heat of substances under isothermal condition is infinite. [During change in state]\\

  3. Specific heat under adiabatic condition is zero[Q=0]\\

  4. Melting point decreases on addition of soluble impurities and increases on\\addition of soluble impurities.\\

  5. Regelation is the process of melting of ice due to increase in pressure and\\ resolidification after removal of pressure.\$

  6. Bottle opened on the moon starts boiling.\\

  7. A large iceberg melts at the base but not at the top because due to high\\pressure, ice at the base lowers its mpt.\\

  8. Generally Cp>Cv but when water is heated from 0-4 Cv>Cp and at 4 degree\\Celsius Cp=Cp.\\

  9. Evaporation decreases temperature.\\

  10. Water is used to cool the radiators of the engine.\\

  11. In high Himalaya it takes longer to cook than in the valley(Because of Pressure).\\

  12. Boiling Water extinguishes fire very quickly.\\

  13. R.H is low in dry air and high in moist air.\\

  14. If the door of the fridge is opened the temperature of the room increases.\\

  15. A man feels hottest when relative humidity is near 100%.\\

  16. Heat required to convert 1 gm of ice at 0 degree Celsius to steam of 100 degree celsius is 716cal.\\

  17. Specific heat of the same substances is expressed in two units C_1 cal/gC and C_2cal/gF then C_1=C_2



Post a Comment