THERMOCHEMISTRY:
HEAT AND TEMPERATURE
• Heat is transferred from a body of Higher
Temperature to one of Lower Temperature
when they are placed in contact.
• Heat and Work are Interconvertable and are
both Forms of Energy
SPECIFIC HEAT
• Specific Heat of System = c s = Cp / m (JK-1 g1)
[C p = Heat capacity of System)]
• For Mass m of Material,
q = Quantity of Heat Absorbed = m cp T
Conversion Factor
1 calorie = 4.184 J
1 calorie = Heat required to raise the Temp.
of 1g of water by 1 0C
Thermochemistry Calculation
• Problem:
Problem (a) Calculate amount of heat
required to raise temperature of 45 kg of
Granite by 15.0 K (b) Replace Granite with
Copper and re-calculate amount of heat
required.
Calculation (contd.)
• (a) Heat absorbed by Granite
= q = mcs (delta)T
= 45 x 103 g x ( 0.82 J /K g) x 15.0 K
= 5.5 x 105 J = 550 kJ
(b) Heat absorbed by Copper
= q = 45 x 10 3 g x (0.385 J/K g) x 15.0 K
= 260 kJ
Bodies at Thermal Equilibrium
• Heat Transfer from Higher Temperature
to Lower Temperature Body.
• At Equilibrium, Heat Gained by Cooler
Body = Heat Lost by Warmer System
• When q is +ve, Heat is Gained by System
• When q is –ve,
ve Heat is Lost by System
• Therefore: q1 = - q2