Chemistry: Energy Unit

Vocab terms from notes for test.

Energy

Capacity for doing work or supplying heat

Potential Energy

Energy that is stored (converted to work or heat)

Kinetic Energy

Energy of motion (related to temperature and heat due to motion of molecules)

Heat

Energy that is transferred from one object or substance to another because of a difference in temperature between them

Thermochemistry

The study of energy changes that occur during chemical reactions and during changes in state

Specific Heat (heat capacity)

Amount of heat required to raise the temperature of 1 gram of a substance by 1°C

Specific Heat

q = (m) (c)( ΔT)

Calorimetry

The measurement of the transfer of heat into or out of a system during a chemical reaction or physical process.

Calorimeter

An insulated container that is used to measure heat change

Energy and Change of State

The stronger the attractions between the molecules in a substance the greater the energy input for phase changes.

System

The specific part of the universe in which we focus our attention (Chemicals)

Surroundings

Everything else besides the system

Exothermic

Heat is released by the system to surroundings (feels warm)

Endothermic

Heat is absorbed by the system (feels cold)

Bond Energy

Is released when bonds form. The same bond energy must be added to break the bonds and separate the atoms again.

Thermochemical equation

A chemical equation that includes the enthalpy change of the reaction.

ΔH

Change in energy during a reaction

If ΔH is positive

The reaction is endothermic

If ΔH is negative

The reaction is exothermic

Endothermic Diagram

Exothermic Diagram

Hess’s Law

Two or more thermochemical equations can be added together to give a final equation.

Hess’s Law: Rule #1

Reverse a chemical → change the sign of ΔH (+ or -)

Hess’s Law Rule #2

If you multiply the equation you multiply the ΔH, too.

Hess’s Law Rule #3

Add up ΔH to determine the ΔH for the overall rxn.

ΔHrxn°

The standard enthalpy of reaction: the change in enthlapy for a reaction carried out under standard conditions.