Chapter 11: Thermal Properties of Matter - Comprehensive NEET Physics Notes

1. Temperature and Heat

1.1 Temperature

• Definition: Temperature is a measure of the 'hotness' of a body.
• Scales: Celsius (°C), Fahrenheit (°F), and Kelvin (K).
• • Conversion: $t_F=\frac{9}{5}{t}_C+32$, $T=t_C+273.15$

Did You Know?

The Kelvin scale is based on absolute zero, the temperature at which molecular motion ceases.

1.2 Heat

• Definition: Heat is the energy transferred between systems or surroundings due to temperature difference.
• Unit: Joule (J).

Common Misconception:

Heat and temperature are often confused. Remember, heat is energy transfer, while temperature is a measure of thermal energy within a body.

2. Ideal-Gas Equation and Absolute Temperature

2.1 Ideal-Gas Law

• Equation: $PV=\mu RT$
• • $P$ = Pressure
  • $V$ = Volume
  • $\mu$ = Number of moles
  • $R$ = Universal gas constant ($8.31,{\text{J mol}}^{-1}{\text{K}}^{-1}$)
  • $T$ = Absolute temperature in Kelvin

Example Application:

Problem: Calculate the pressure of 2 moles of an ideal gas at a temperature of 300 K in a volume of 10 L. Solution: Use the ideal gas law: $P=\frac{\mu RT}{V}=\frac{2\times 8.31\times 300}{0.01}=4986,\text{Pa}$

3. Thermal Expansion

3.1 Linear Expansion

• Formula: $\frac{\Delta l}{l}={\alpha }_l\Delta T$
• • $\Delta l$ = Change in length
  • $l$ = Original length
  • ${\alpha }_l$ = Coefficient of linear expansion
  • $\Delta T$ = Temperature change

3.2 Volume Expansion

• Formula: $\frac{\Delta V}{V}={\alpha }_V\Delta T$
• • $\Delta V$ = Change in volume
  • $V$ = Original volume
  • ${\alpha }_V$ = Coefficient of volume expansion

NEET Problem-Solving Strategy:

To solve expansion problems, ensure that the correct expansion coefficient (linear, area, or volume) is used depending on the problem.

4. Specific Heat Capacity

4.1 Specific Heat Capacity (s)

• Formula: $s=\frac{1}{m}\frac{\Delta Q}{\Delta T}$
• • $\Delta Q$ = Heat added
  • $m$ = Mass
  • $\Delta T$ = Temperature change

4.2 Molar Specific Heat Capacity (C)

• Formula: $C=\frac{1}{\mu }\frac{\Delta Q}{\Delta T}$
• • $\mu$ = Number of moles

Mnemonic:

Remember “Q = mcΔT” as "Quick! Call Doctor T!" to recall the formula for heat transfer.

5. Latent Heat

5.1 Latent Heat of Fusion (Lf) and Vaporization (Lv)

• Formula: $Q=mL$
• • $L_f$ = Latent heat of fusion (for solid to liquid)
  • $L_v$ = Latent heat of vaporization (for liquid to gas)

Common Mistake:

Students often forget that during a phase change, temperature remains constant. Use latent heat formulas instead of specific heat during these processes.

6. Heat Transfer

6.1 Conduction

• Formula: $H=\frac{KA(T_C-T_D)}{L}$
• • $H$ = Heat transfer rate
  • $K$ = Thermal conductivity
  • $A$ = Cross-sectional area
  • $L$ = Length
  • $T_C,T_D$ = Temperatures at ends

6.2 Convection and Radiation

• Convection: Heat transfer via fluid movement.
• Radiation: Heat transfer via electromagnetic waves.

Real-life Application:

Insulating materials in houses reduce conduction, convection, and radiation losses, maintaining thermal comfort.

Quick Recap

• Temperature is a measure of hotness.
• Ideal-gas law: $PV=\mu RT$.
• Thermal expansion: Linear, area, and volume.
• Specific heat capacity: Amount of heat per unit mass for a temperature change.
• Latent heat: Heat required for phase change.
• Heat transfer: Conduction, convection, and radiation.

Practice Questions

1. A gas occupies a volume of 0.5 m³ at a pressure of 100 kPa and a temperature of 300 K. Calculate its volume at 600 K if the pressure remains constant.
2. An iron rod of length 1 m is heated from 20°C to 100°C. Calculate its change in length. (${\alpha }_l$ for iron = $1.2\times 10^{-5},{\text{K}}^{-1}$).
3. How much heat is required to convert 2 kg of ice at 0°C to water at 0°C? ($L_f$ for water = $3.33\times 10^5,{\text{J kg}}^{-1}$).
4. A calorimeter contains 0.1 kg of water at 25°C. If 0.05 kg of steam at 100°C is passed into it, what will be the final temperature of the water?
5. Explain Newton's law of cooling and calculate the rate of cooling if the difference in temperature between the body and the surroundings is 50°C.

Solutions:

1. $V_2=\frac{V_1{T}_2}{T_1}=\frac{0.5\times 600}{300}=1,{\text{m}}^3$
2. $\Delta l=l{\alpha }_l\Delta T=1\times 1.2\times 10^{-5}\times 80=0.00096,\text{m}$
3. $Q=m{L}_f=2\times 3.33\times 10^5=666000,\text{J}$
4. Solution involves calorimetry equations.
5. Solution involves applying Newton's cooling law formula.

Glossary

• Temperature: A measure of thermal energy.
• Heat: Energy transfer due to temperature difference.
• Thermal Expansion: Increase in size of a material with temperature.
• Specific Heat Capacity: Heat needed to raise the temperature of a unit mass by 1°C.
• Latent Heat: Heat required for a phase change without temperature change.

These notes offer a focused and organized summary of the chapter "Thermal Properties of Matter," ensuring NEET aspirants have all necessary formulas and concepts for effective preparation.