thermo

Chapter 15
(not much on E)

Thermodynamics:
Enthalpy, Entropy
& Gibbs Free
Energy

Thermo 2

Thermodynamics:

thermo = heat (energy) dynamics = movement, motion

Some thermodynamic terms chemists use:
System: the portion of the universe that we are considering open system: energy & matter can transfer closed system: energy transfers only isolated system: no transfers
Surroundings: everything else besides the system
Isothermal: a system that is kept at a constant temperature by adding or subtracting heat from the surroundings. Heat Capacity: the amount of heat energy required to raise the temperature of a certain amount of material by
1°C (or 1 K).
Specific Heat Capacity: 1 g by 1°C
Molar Heat Capacity: 1 mole by 1°C

Thermo 3

Calorie: the amount of heat required to raise the temperature of 1g of water by 1°C. specific heat of water = 1 cal/g °C

1 calorie = 4.18 joules
Specific Heats and Molar Heat Capacities
Substance

Specific Heat (J/°Cg)

Molar Heat (J/°Cmol)

Al
Cu
Fe
CaCO3

0.90
0.38
0.45
0.84

24.3
24.4
25.1
83.8

Ethanol

2.43

112.0

Water

4.18

75.3

Air

1.00

~ 29

important to:

engineers

chemists

EXAMPLE: How many joules of energy are needed to raise the temperature of an iron nail (7.0 g) from 25°C to 125°C?
The specific heat of iron is 0.45 J/°Cg.
Heat energy = (specific heat)(mass)(T)
Heat energy = (0.45 J/°Cg)(7.0 g)(100°C) = 315 J
Note that T can be ºC or K, but NOT ºF. When just T is being used in a scientific formula it will usually be kelvin (K).

Thermo 4

Problem: How much energy does it take to raise the body temperature 2.5ºC (a fever of just over
103ºF) for someone who weighs 110 pounds (50 kg).
Assume an average body specific heat capacity of
3 J/ºC.g.

Problem: What would be more effective at melting a frozen pipe – hot water or a hair dryer (hot air gun). Why?

Thermo 5

State Functions
System properties, such as