Chem 1150 - Energy, Heat, & Enthalpy Lecture Notes

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Thermodynamics

Area of science that deals with the interconversion of heat and other forms of energy

Thermochemistry

The absorption or release of energy that accompanies chemical reactions

Potential energy is stored within molecules

Kinetic energy is the motion of the molecules

Temperature

Measure of average kinetic energy of the atoms/molecules that make up the substance

Heat (q)

Amount of kinetic energy that is transferred spontaneously from a hotter object to a colder object through atomic/molecular collisions

Heat = thermal motion, temperature is a measure of that motion

Potential Energy

Dependent on the identity of the substance and quantity of mols (identity with more molar mass or substance with more mols = higher P.E.)

Internal Energy (E)

Sum of all kinetic and potential energies of every molecule/ion within a system

1^st Law of Thermodynamics

Total internal energy of an isolated system is constant

Exothermic Reaction

Reaction in which energy flows out of the system and into the surroundings as a result of energy being released by the reactants. (lost as heat)

Endothermic Reaction

Reaction in which energy flows into the system from its surroundings and is absorbed by the reactants and stored within the products

Enthalpy (ΔH)

The heat transfer for a reaction when pressure is constant

Standard Thermodynamic State

Substance’s most stable form at 1 atm of Pressure

Temperature at 298.15 K or 25 Degrees Celsius

1 M concentration for all species in solution

Heat Capacity (C)

The heat required to raise the temperature of a sample by a given amount (Joules/Degrees Celsius)

C = q /ΔT

q = C*ΔT

ΔT = T_final - T_initial

Molar Heat Capacity (C_m)

Amount of heat necessary to raise the temperature of one mole of a substance by 1°C

q = C_m * ΔT * moles of substance

Amount of heat necessary to raise the temperature of one gram of substance by 1°C

q = s * ΔT * grams of substance

or q = mass * sΔT