Unit 12 Chemistry Honors: Energy

Thermochemistry

Relationships between chemical reactions and energy changes that involve heat.

Energy

The capacity to do work or transfer heat.

Joules (J) are a…

SI Unit

Work

Energy used to cause an object to move against a force.

Heat

Energy used to cause the temperature of an object to increase.

Temperature

Measures the intensity of heat (average kinetic energy of the particles).

The universe is divided into two parts—

The system and the surroundings

The system

The reactants and products in a reaction—where we focus in chemistry

The surroundings

Everything else in the universe

Endothermic (+)

Energy comes into the system (feels cold).

Exothermic (-)

Energy comes out of the system (feels hot).

Energy changes are due to…

The changes in potential energy that occurs during the course of a reaction.

Calories (cal) are…

Non SI Units

Heat + work =

Change in energy

Calorimetry

Measuring the amount of heat energy transferred.

1st Law of Thermodynamics

Energy cannot be created or destroyed.

Specific Heat

Measures the amount of heat needed to change 1 gram of a substance by 1 Kelvin or degree Celsius.

Specific Heat Equation

Q = mc 🔼T

Energy Conservation Equation

(Use when you have two different elements)

E = -E

Heat of Fusion Equation

Key word: melting

Q = (m) (🔼Hf)

Heat of Vaporization Equation

Key words: boiling, steam

Q = (m) (🔼Hv)

Heating Curve Graph

Enthalpy (🔼H)

The quantity of energy transferred as heat during a chemical reaction.

Enthalpy depends on the amount of _____ present; extensive property

Substances

Thermochemical Equation

(Shows the Enthalpy change)

Enthalpy change occurs when…

One mole of a compound is formed from its elements in their standard state.

Each compound has its own…

Standard heat of formation

The heat of formation of an element is equal to…

Zero

Negative heat of formations are…

Stable

Positive heat of formations are…

Unstable

Change in Enthalpy Equation

🔼H = (products) - (reactants)

Hess’s Law

(Make the givens look like the wanted product)

• Whatever you do to your reaction, do the same to your empathy change.

Entropy (S)

The measure of randomness of the components of the universe.

• randomness ⬆, entropy ⬆

2nd Law of Thermodynamics

The entropy of the universe is always increasing.

Spontaneous Process

Occurs in nature without outside interventions.

(A process is spontaneous only if the entropy of the universe increases as a result of the process.)

• (+) Spontaneous, entropy ⬆

Gibbs’s Free Energy

• The combined enthalpy-entropy function

Processes in nature are driven in two directions; towards least enthalpy and toward largest entropy.

(The dominant factor determines the direction of change)

Spontaneous reactions are…

(-)

Nonspontaneous reactions are…

(+)

Gibbs’s Free Energy Equation

🔼G = 🔼H - T(🔼S)