Chemistry Chapter 17: Thermochemistry

heat

Represented by q. The quantity of energy that transfers from one object to another because of a temperature difference between them.

Heat always flows from \____ to \____

A warmer object to the cooler object (it is NEVER flowing from cold to hot)

Thermochemistry

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

Chemical potential energy

Energy stored in chemical bonds

endothermic process

the system gains heat as the surroundings cool down

Exothermic process

the system loses heat as the surroundings heat up

Law of Conservation of Energy

In any chemical or physical process, energy is neither created nor destroyed.

Calorie

Amount of energy needed to raise temperature 1 gram of water 1 degree C

Joule

SI unit of energy

heat capacity

the number of heat units needed to raise the temperature of a body by one degree. (q)

specific heat

The amount of energy required to raise the temperature of 1 gram of a substance by 1 degree celcius

specific heat equation

c \= q/mΔT

Calorimetry

The precise measurement of heat flow out of a system for chemical and physical processes

The heat released by the system is equal to

heat absorbed by surroundings

calorimetry equation

qsystem \= -qsurroundings \= ΔH \= -m x C x ΔT

Calorimeter

an insulated device used to measure the absorption or release of heat in chemical or physical processes

Enthalpy

The heat content of a system at constant pressure

thermochemical equation

a chemical equation that includes the amount of heat produced or absorbed during the reaction (enthalpy change)

How does the quantity of heat absorbed by a melting solid compare to the quantity of heat released when the liquid solidifies?

the quantity of heat absorbed by a melting solid is exactly the same as the quantity of heat released when the liquid solidifies

molar heat of fusion (ΔHfus)

The heat absorbed by one mole of solid substance as it melts to a liquid at a constant temperature

molar heat of solidification (ΔHsolid)

The heat lost when one mole of a liquid solidifies at a constant temperature

Heats of Fusion and Solidification equation

q \= mLfus (latent heat of fusion, a constant)

How does the quantity of heat absorbed by a vaporizing liquid compare to the quantity of heat released when the vapor condenses?

the quantity of heat absorbed by a vaporizing liquid is exactly the same as the quantity of heat released when the vapor condenses

molar heat of vaporization (ΔHvap)

The amount of heat necessary to vaporize one mole of a given liquid

molar heat of condensation (ΔHcond)

The amount of heat released when one mol of vapor condenses at the normal boiling point

Heats of Vaporization and Condensation Equation

q \= mLvap (latent heat of vaporization)

During the formation of a solution, heat is

Either released or absorbed.

molar heat of solution (ΔHsoln)

The enthalpy change caused by dissolution of one mole of substance

Hess's law of heat summation

if you add two or more thermochemical equations to give a final equation, then you also add the heats of reaction to give the final heat of reaction

standard heat of formation (ΔH°f)

The change in enthalpy that accompanies the formation of one mole of a compound from its elements with all substances in their standard states at 25 degrees Celsius.