unit 6: thermodynamics

heat (thermal energy/q)

a measure of heat transfer when a colder object is in contact with a hotter object (heat goes from hot object → into cold object)

temperature (celsius, kelvin)

measure of average kinetic energy in an object/material

enthalpy (ΔH)

measure of the internal energy of the system + the work (E + W). ΔH = Energy + (Pressure)(Volume)

internal energy (E)

energy required to reach a certain state from from a defined “standard” state

endothermic processes/reactions

the system has a net energy gain (takes energy from the surroundings to complete). result in higher energy (less stable) particle configuration). absorb energy when reacting

breaking chemical bonds . . .

is an endothermic process

exothermic processes/reactions

result in a net release of energy from the system into the surroundings. result in lower energy (more stable). releases heat when reacting

making chemical bonds . . .

is an exothermic process

ΔH(rxn) =

(ΔH[products] - ΔH[reactants])

thermal equilibrium

there is no net change in heat/temperature for either materal (rate of heat transfer is equal)

q =

mcΔt

• q = heat transferred

• m = mass (in grams)

• c = heat capacity of material

• Δt = change in temperature (final - initial)

enthalpy of reaction/heat of reaction (ΔH(rxn))

(ΔH(rxn)) the difference in energy between products and reactants. endothermic bond enthalpies are positive +, exothermic bond enthalpies are negative -

standard enthalpy of formation (ΔH(f))

the change in energy when . . .

1. 1 mole of some compound is formed

2. at standard temperature & pressure

3. from its’s elemental components as they exist in the above conditions

4. NO FRACTIONS IN PRODUCTS

ΔH(rxn) =

ΔH(f)[products] - ΔH(f)[reactants]

bond enthalpy equation: ∆H(rxn) =

sum of energy required to break bonds - sum of energy required to make bonds

hess’s law

if a reaction occurs in a series of steps, ∆H for the overall reaction is equal to the sum of ∆H of the individual steps

calorimetry

an experimental technique used to calculate the energy lost or gained in a physical/chemical experiment