Chem 1100- Thermodynamics

Energy

the ability to do work

Kinetic energy

the energy of movement

• Ekinetic= 1/2m(v2)

Potential energy

stored energy

• ex: Gravitational energy

Electrical energy

• energy from molecular charges (like repel, opposites attract)

Chemical energy

• Energy from bond creation and destruction

High potential energy within a molecule

Molecule is not stable

Low potential energy within a molecule

Molecule is relatively stable

Potential energy increases within an atom as…

electrons are pulled away from the nucleus (ionic radii)

Bond formation

Releases energy (exothermic)

Bond breakage

Takes in energy (endothermic)

Thermal energy

Total kinetic energy within a sample responsible for temperature

Molecular movement

• Translational (linear)

• Rotational (spins)

• Vibrational (movements of atoms within their molecular bonds, intramolecular)

Radiant energy

Energy contained in electromagnetic radiation (light)

Thermodynamics

study of energy transfers and transformations

First law of thermodynamics

Energy is neither created nor destroyed, although it may be transformed into different forms of energy

Heat

When a system exchanges thermal energy with its surroundings (energy transferred between atoms/molecules)

Changes in temperature depend on (4 things):

1. Heat flow

2. Amount of heat transferred

3. Material involved

4. Amount of material involved

Molar heat capacity

J/mol x C

Heat capacity

J/C

Specific heat

J/g x C

System does work on surroundings

-w

surroundings do work on system

+w

Energy is transferred between a sys/surr in which ways?

• work

• energy

State functions

The net change is wanted, path taken to achieve result is not cared for

ex: enthalpy, energy

Path function

how change occurs in a system during a transformation, path taken to achieve result is wanted

ex: work, heat

Stable reactant —> unstable product

endothermic (photosynthesis)

unstable reactant—→ stable product

exothermic (ATP)

Bond energies

Positive quantities of energy required to break a bond (energy/mol required to break a agas molecule into a pair of neutral gas fragments)

Calorimeter

An insulated device used to measure heat flows that accompany chemical reactions.

Constant pressure, changing volume (good for gases)

Constant volume, changing pressure (good for solutions)

Enthalpy

thermodynamic function that describes heat flow at a constant pressure

Expansion work

We generally assume everything is done at a constant pressure (1 atm) on Earth, and let volume change

Formation reactions

a reaction which uses 1 mol of a compound to form chemical elements in their standard state

Formation state

The most basic/neutral state of a substance (what it is at room temperature in standard conditons)

Heat

Energy transferred between objects, the energy needed to move and object against an opposing force

An element that is in a state different from its standard state has a ___ enthalpy

positive

An element already in its standard state has an enthalpy of ____

0

Hess’s law

the total enthalpy change for a chemical reaction is the same whether it occurs in one step or several steps, as long as the initial and final states of the reactants and products are the same

Enthalpy of formation of a substance depends on its ____

phase, because heat is required to melt/boil a substance