Specific Heat and Calorimetry

Thermodynamics aur heat transfer ke important topics me se ek Specific Heat aur Calorimetry hai. Ye concepts materials ke thermal behavior ko quantify karte hain aur heat energy ke exchange ko measure karne me madad karte hain.

1. Introduction

Heat aur temperature ke concepts ke baad, hum samajhte hain ki different materials heat energy ko kaise absorb ya release karte hain.

Specific Heat: Ek material ki ability hoti hai ki woh unit mass par 1°C ya 1 K temperature change ke liye kitna heat absorb ya release karta hai.
Calorimetry: Science of measuring heat transfer between system aur surroundings.

Ye concepts engineering, physics aur chemistry me fundamental hain, aur daily life applications me bhi use hote hain, jaise cooking, heating systems, aur material processing.

2. Specific Heat

2.1 Definition

Specific heat (c) define kiya jata hai as:

The amount of heat energy required to raise the temperature of 1 kg of a substance by 1°C (or 1 K).

Mathematically: Q=mcΔTQ = m c \Delta TQ=mcΔT

Where:

QQQ = heat absorbed/released (Joules)
mmm = mass of the substance (kg)
ccc = specific heat capacity (J/kg·K)
ΔT\Delta TΔT = change in temperature (K or °C)

Unit: Joule per kilogram per Kelvin (J/kg·K)

2.2 Importance of Specific Heat

Determines how much energy a substance can store or release.
Crucial for thermal management in engineering applications.
Explains why water is used as a coolant: High specific heat → absorbs large amount of heat with small temperature change.

2.3 Specific Heat of Common Substances

Substance	Specific Heat (J/kg·K)
Water	4186
Ice	2090
Aluminum	900
Copper	385
Iron	450
Lead	128

Observation: Metals have low specific heat, liquids like water have high specific heat.

2.4 Factors Affecting Specific Heat

Material type: Metals vs Non-metals
State of matter: Solid, liquid, gas
Temperature range: Specific heat may vary with temperature
Pressure: Usually minor effect for solids and liquids

3. Heat Capacity

Heat Capacity (C) is related concept:

Definition: Amount of heat required to raise the temperature of an object by 1°C.
Formula:

C=mcC = m cC=mc

Where mmm is mass of the object and ccc is specific heat.

Unit: J/K
Difference from Specific Heat: Heat capacity depends on mass, specific heat is per unit mass.

4. Calorimetry

4.1 Definition

Calorimetry is the science of measuring the heat exchanged during chemical or physical processes.

Devices used: Calorimeters
Principle: Heat lost by hot body = Heat gained by cold body (assuming no loss to surroundings).

Mathematical expression: Qlost=QgainedQ_{lost} = Q_{gained}Qlost=Qgained

4.2 Types of Calorimeters

Coffee Cup Calorimeter (Constant Pressure)
- Simple, used in chemistry labs.
- Measures heat of reactions in liquids.
Bomb Calorimeter (Constant Volume)
- Used for combustion reactions.
- Measures calorific value of fuels.
Differential Scanning Calorimeter (DSC)
- Measures heat flow as a function of temperature.

4.3 Principle of Calorimetry

Law of Heat Exchange:

When two bodies at different temperatures are brought in contact in an isolated system, heat lost by the hotter body = heat gained by the cooler body.

Mathematically: m1c1(T1−Tf)=m2c2(Tf−T2)m_1 c_1 (T_1 – T_f) = m_2 c_2 (T_f – T_2)m1c1(T1−Tf)=m2c2(Tf−T2)

Where:

m1,m2m_1, m_2m1,m2 = masses
c1,c2c_1, c_2c1,c2 = specific heats
T1,T2T_1, T_2T1,T2 = initial temperatures
TfT_fTf = final equilibrium temperature

4.4 Experimental Determination of Specific Heat

Step 1: Measure mass of substance (mmm)
Step 2: Heat the substance to known temperature (T1T_1T1)
Step 3: Place it in calorimeter with known mass of water at temperature (T2T_2T2)
Step 4: Measure final temperature (TfT_fTf)
Step 5: Apply formula: mc(T1−Tf)=mwatercwater(Tf−T2)m c (T_1 – T_f) = m_{water} c_{water} (T_f – T_2)mc(T1−Tf)=mwatercwater(Tf−T2)

Example Calculation:

100 g of metal at 100°C placed in 200 g water at 25°C
Final temperature = 30°C
Calculate specific heat of metal

0.1c(100−30)=0.2(4.186)(30−25)0.1 c (100-30) = 0.2 (4.186)(30-25)0.1c(100−30)=0.2(4.186)(30−25) 0.1c(70)=0.2(4.186)(5)0.1 c (70) = 0.2 (4.186)(5)0.1c(70)=0.2(4.186)(5) 7c=4.1867 c = 4.1867c=4.186 c≈0.598 kJ/kg\cdotpK =598J/kg⋅Kc \approx 0.598 \text{ kJ/kg·K } = 598 J/kg·Kc≈0.598 kJ/kg\cdotpK =598J/kg⋅K

5. Calorimetry in Chemistry

Heat of neutralization, dissolution, and reaction are measured using calorimeters.
Exothermic reaction: Releases heat → raises temperature of calorimeter.
Endothermic reaction: Absorbs heat → lowers temperature.

6. Specific Heat in Daily Life

Cooking: Food heats faster with low specific heat material.
Climate: Water bodies moderate climate due to high specific heat.
Thermal Storage: Materials with high specific heat used in thermal energy storage.

7. Graphical Representation

Temperature vs Heat Graph

T
|
|       ----
|      / 
|     / 
|    /
|   /
|  /
| /
|/________________ Q

Slope = 1/(m·c)
Plateau indicates phase change (melting/boiling)

8. Relation to Phase Changes

During phase change, temperature remains constant while substance absorbs or releases latent heat.

Heat for phase change:

Q=mLQ = m LQ=mL

Where LLL = latent heat (fusion or vaporization)

Calorimetry accounts for both specific heat and latent heat.

9. Practical Applications of Calorimetry

Food Industry: Determine calorific value of foods.
Fuel Industry: Measure energy content of fuels.
Material Science: Study thermal properties of metals, alloys, polymers.
Environmental Science: Measure heat exchange in ecosystems.

10. Summary Table

Concept	Definition/Formula	Unit
Specific Heat (c)	Q=mcΔTQ = m c \Delta TQ=mcΔT	J/kg·K
Heat Capacity (C)	C=mcC = m cC=mc	J/K
Calorimetry	Measurement of heat transfer	Joules (J)
Law of Heat Exchange	Qlost=QgainedQ_{lost} = Q_{gained}Qlost=Qgained	Joules (J)
Latent Heat (L)	Q=mLQ = m LQ=mL	J/kg