The first law of Thermodynamics (chapter 5)

System

Part of the universe chosen to study ( for a chemist: chemical reactions )

Surroundings

The rest of the universe

Open system

Freely exchanges energy and matter with its surroundings(ex: like a glass beaker)

Closed System

Can exchange energy, but not matter with its surroundings(ex: stoppered flask)

Isolated System

Cannot exchange energy or matter with its surroundings(ex: a thermist)

Energy

The capacity to do work

The SI unit for work

Joule (J) kg m2 s-2

Work

Force acting over a distance

Kinetic energy

The energy of a moving object

Thermal energy

Kinetic energy associated with random molecular motion

Potential energy

Energy resulting from condition, position, or composition

Chemical energy

Potential energy stored in the bonds of chemical compounds

First law of thermodynamics (law of conservation of energy)

States energy can be converted from one form to another, but cannot be created or destroyed.

Internal Energy

The internal energy of a system(U) is the sum of all potential and kinetic energies in the system

Heat

The transfer of thermal energy between a system and surroundings due to a temperature difference

The amount of energy of heat(a) needed to change the temperature depends on:

• How much the temperature changes

• The quantity of the substance

• The nature of the substance

The SI unit for heat

Joule

Functions of state

Any property that has a unique value for a specific state

The state of the system is described by:

It’s temperature, pressure, and the kinds and amounts of substances present

Path independent

A state function that does not depend on how that state was established(ex: Internal energy(U))

Path dependent Functions

Depend on the path taken when a system undergoes a change(Ex: Heat and work)

Enthalpy

• The change in energy of a system at constant pressure

• The sum of the change in internal energy and the pressure-volume product

• equal to heat at a constant pressure

• A measure of the energy stored in chemical

Endothermic reaction

Positive; heat has entered the system

Exothermic reaction

Negative; heat has exited the system