19.1 Student Notes

I. First Law of Thermodynamics; Enthalpy

A. Background

1. Thermodynamics –

2. Enthalpy –

B. First Law of Thermodynamics; Enthalpy

1. Internal Energy – U –

a. Kinetic energy –

b. Potential energy –

2. State function –

3. Work –

4. Work done on the system is positive ( )

Work done by the system is negative ( )

5. ΔU = q + w

First law of thermodynamics –

C. Heat of Reaction and Internal Energy

1. w =

w –

P -

V –

2. Consider the combustion (burning) of methane, CH₄, in oxygen.

CH₄ (g) + 2 O₂ (g) à CO₂ (g) + 2 H₂O (l)

The heat of reaction at 25° C and 1.00 atm is – 890.2 kJ. What is the change in volume when 1.00 mol CH₄ reacts with 2.00 mol O₂? (You can ignore the volume of liquid water, which is insignificant compared with volumes of gases.) What is w for this change? Calculate ΔU for the change indicated by the chemical equation.

D. Enthalpy and Enthalpy Change

1. Def –

2. State function

3. ΔH° =

4. Exothermic =

Endothermic =