Chem 2: Thermochemistry (pdf)

Energy

capacity to do work

work

chemistry defined this as directed energy change resulting in process.

radiant energy

also called solar energy, comes form the sun and is Earth's primary energy source.

thermal energy

energy associated with the random motion of atoms and molecules.

chemical energy

is stored within the structural units of chemical substances

potential energy

energy available by virtue of an object's position

Heat

the transfer of thermal energy between two bodies that are at different temperatures.

Thermochemistry

the study of heat change in chemical reactions

System

the specific part of the universe that is of interest to us.

Surrounding

the rest of the universe outside the system

Open system

can exchange mass and energy, usually in the form of heat with its surroundings

closed system

allows the transfer of energy (heat) but not mass

isolated system

which does not allow transfer of either mass or energy

state functions

properties that are determined by the state of the system, regardless of how that condition was achieved

(where only the start and end points matte rather than the path taken)

ex: energy, pressure, volume, and temperature

FIRST law of thermodynamics

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

only the change in internal energy of a system between its initial state and its final state in a process.

∆(u) = (u)f - (u)i

we can test the validity of the first law by measuring?

∆(u) = q t w

formula in measuring energy (with heat as q, work as w), since we are normally interested in the energy changes associated with the system.

Heat (q)

energy that is transferred from one body to another as the result of a difference in temperature

Work (w)

is the energy transferred to or from an object via the application of force along a displacement

sign conventions for work and heat

used to determine the sign to be used when calculating/evaluating the work done as well as heat.

negative sign

work done BY the system ON the surroundings;

heat absorbed by the SURROUNDINGS from the SYSTEM (EXOTHERMIC process)

positive sign

work done ON the system BY the surroundings;

heat absorbed by the SYSTEM from the SURROUNDINGS (ENDOTHERMIC process)

mechanical work

in thermodynamics, work has broader meaning that includes ____. An examples of this is a combustion engine in automobiles.

w = -P∆V

As it expands, the gas pushes the piston upward against a constant opposing external atmospheric pressure P.

The work done by the gas on the surrounding is:

liter atmospheres

the unit for work done by or on a gas