Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 1

Some Forms of Energy

- Solar Energy, part of radiant energy. Solar energy comes from the Sun and is the primary source of Earth’s energy. - Thermal Energy is due to random motion of atoms and molecules. It is generally calculated from temperature measurements. Temperature is not a measure of thermal energy itself. - Chemical Energy is stored within the structural units of chemical substances. When a chemical reaction takes place, chemical energy is released, stored, or converted to other forms of energy. - Potential Energy is the energy due to the position of an object. Chemical energy can be considered to be a form of potential energy, since it is associated with the positions of atoms in the molecules. - Kinetic Energy is the energy produced by a moving object.

Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 2

System-Boundary-Surroundings

ImaginaryBoundary Im

aginary

BoundaryIm

agin

ary

Bou

ndar

y

ImaginaryBoundary

The boundary might be imaginary, as in this case, or real, as in other cases.

Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 3

Three Types of Systems

Open: energy anmass can beexchanged

Closed: onlyenergy can beexchanged

Isolated: nothing is exchanged

Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 4

An Example to State Functions – Distance vs. Displacement

A

B

There are many routes between A and B. The distance covered by the coloured routes is different from one another. The displacement, however, is the same for all routes, AB.

Displacement is a state function, whereas distance is not.

Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 5

Another Example of a State Function- Volume

A I1

I2 B

Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 6

The First Law of Thermodynamics

System

Surroundings Universe

Energy Out

It is obvious that, energy lost by the system is absorbed by the surroundings. Since the Universe comprises both the system and the surroundings, energy is conserved in the process.

Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 7

Sign Convention for Work and Heat

Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 8

Expansion of a Gas in a Cylinder

Initial State Final State

Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 9

Bomb Calorimeter

The thermometer is used to determine t of the reaction. qcal is calculated from

cal calq C t

Thermochemistry

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 10

An Open Calorimeter

The thermometer is used to determine t of the reaction. q is calculated from

q ms T