Chem Chap 6

Thermochemistry

study of heat transfer in chemical reactions and physical changes

Energy

ability to do work or transfer heat

Work (w)

energy used to move an object

Heat (q)

energy transfer accompanied by change in temperature

System

everything involved in the reaction or change observed

Surroundings

everything not in the system

Universe

the system and surroundings

Enthalpy

energy in a thermodynamic system

Kinetic energy

energy due to motion

KE =

½ mv²

SI unit for KE

joule

Joule abbreviation

J

J =

kg x m²/s²

Potential energy

energy due to position (always relative to something)

Electrostatic Potential Energy

energy due to positions of charged particles

PE_el =

(kQ₁Q₂)/d

In (kQ₁Q₂)/d, k =

constant (varies with material between particles)

In (kQ₁Q₂)/d, Q =

charge

In (kQ₁Q₂)/d, d =

distance on center

When Q₁Q₂ > 0 (like charges, repulsion)

E_el decreases and approaches 0 as distance approaches positive infinity

When Q₁Q₂ < 0 (opposing charges, attraction)

E_el increases and approaches 0 as distance approaches positive infinity

Temperature

measure of average internal KE

Exception to heat

heat can be transferred without temperature change during phase changes

Internal Energy (E) of a system

sum of all kinetic and potential energies of everything in the system

Is E a fixed or not fixed value

Not a fixed value

First Law of Thermodynamics

energy is neither created nor destroyed

Exergonic

system internal energy decreases

Endergonic

system internal energy increases

Energy is exchanged between system and surroundings as

heat (q) and work (w)

State functions

depend on the state of a system, NOT how the system arrived at that state

Example of state function

Internal energy

Not example of state function

heat and work

Exothermic

system loses heat (q<0)

Endothermic

system gains heat (q>0)