Thermochemistry Lecture Notes

These flashcards cover key terms and concepts from the Thermochemistry lecture notes, including definitions and important laws related to energy transfer, thermal chemistry, and calorimetry.

Energy

The ability to supply heat or do work.

Potential energy

The energy something has because of its position, composition, or condition.

Kinetic energy

The energy an object has because of its motion.

Law of conservation of energy

Energy cannot be created or destroyed, only transferred or transformed.

Thermal energy

A kind of kinetic energy associated with the random motion of atoms and molecules.

Temperature

A quantitative measure of 'hot' or 'cold', with fast molecules indicating high thermal energy and slow molecules indicating low thermal energy.

Heat

The transfer of thermal energy between two bodies at different temperatures.

Exothermic heat

Heat that is released.

positive

Endothermic heat

Heat that is absorbed.

negative

Heat capacity (C)

The amount of heat absorbed or released when its temperature changes by 1°C or 1K.

Calorimetry

The measurement of the amount of heat transferred to or from a substance.

net change of heat

0

qsys = -qsurr

Internal energy (U or E)

Total of all possible kinds of energy in a substance.

state function

• the value only matters, not how you got there

path function

their values depend on how the system reaches that state

heat and work are examples

First Law of Thermodynamics

Energy is conserved; energy change in a system is equal to the heat added to the system minus the work done by the system.

work decreases for the thing doing the work

Expansion (pressure) work

a system pushes against the surroundings, or surroundings compress the system

Enthalpy (H)

The sum of internal energy plus pressure multiplied by volume.

only for chemical/physical processes, not specific substances

Standard State (°)

Commonly accepted set of conditions for thermodynamic measurements, including a pressure of 1 bar and a concentration of 1 M.

Standard enthalpy of formation

The enthalpy change when exactly 1 mole of a substance is formed from its free elements in their most stable states under standard conditions.

thermochemical equations

represents changes in both matter and energy during a chemical reaction

enthalpy changes if the state of a reactant or product changes, or if any part of the equation changes

if coefficients of eq’n multiplied

enthalpy is also multiplied by this

enthalpy of a reaction depends on

the physical states of the reactant and products

Hess’ Law

The enthalpy change of an overall reaction equals the sum of the enthalpy changes of the individual steps of the reaction.