Chapter 6 - Thermochemistry

Thermochemistry

Study of energy exchange in chemical/physical changes.

Energy

Capacity to do work.

Potential Energy

Energy due to position or composition.

Kinetic Energy

Energy due to motion.

Thermodynamics

Study of energy and energy transformations.

System

Part of the universe being studied.

Surroundings

Everything outside the system.

Universe

System + Surroundings.

Internal Energy (E)

Sum of kinetic and potential energies in a system.

ΔE

Change in internal energy = Efinal - Einitial.

First Law of Thermodynamics

Energy is conserved; ΔEuniv = ΔEsys + ΔE_surr = 0.

Heat (q)

Energy transferred due to temperature difference.

Work (w)

Energy transfer by force/motion (e.g., expansion).

ΔE formula

ΔE = q + w

Sign of q

• if heat gained, - if heat lost.

Sign of w

• if work done on system, - if by system.

Energy unit

Joule (J)

1 J

1 J = 1 kg·m²/s²

Calorie

1 cal = 4.184 J

Nutritional Calorie

1 Cal = 1000 cal = 1 kcal

State Function

Property depending only on current state, not path (e.g., ΔE, T, P).

PV Work

w = –PΔV

Enthalpy (ΔH)

Heat change at constant pressure; ΔH = q_p.

ΔH formula

ΔH = Hproducts - Hreactants

Exothermic

Releases heat; ΔH < 0

Endothermic

Absorbs heat; ΔH > 0

Specific Heat (c)

Heat to raise 1 g of substance by 1°C or 1 K.

Molar Heat Capacity

Heat to raise 1 mol of substance by 1°C or 1 K.

Specific Heat of Water

c = 4.184 J/g·K = 1 cal/g·K

Heat Formula

q = c × m × ΔT

Calorimeter

qreaction = –qH₂O

Thermochemical Equation

Includes ΔH value in balanced equation.

Hess’s Law

ΔH_total = sum of ΔH of steps.