Calorimetry and First Law of Thermodynamics

heat capacity (C)

amount of energy needed to raise the temperature of an object by 1C; Q = C∆T

specific heat capacity (Cp)

amount of heat required to raise the temperature of 1g of a substance by 1C; Q = mCp∆T

calorimetry

scientific technique and measurement method used to determine the amount of heat energy transferred in a chemical reaction or physical process

endothermic reaction

∆H>0

exothermic reaction

∆H<0

constant-pressure calorimetry

constant pressure, energy may be transferred as heat and as expansion work; coffee-cup calorimeter

constant-volume calorimetry

cheat released during the reaction is absorbed by the calorimeter, heat absorbed is related using its heat capacity; combustion of reaction if involved; bomb calorimeter

Q = C∆T

heat capacity (C)

∆Hrxn = Qrxn = ∆Erxn

constant-volume calorimetry

Q = mCp∆T

specific heat capacity (Cp)

∆Hrxn = Qrxn = -Qmixture - Qcal

constant-pressure calorimetry

Zeroth Law of Thermodynamics

if two bodies are each in thermal equilibrium

(same temperature) with some third body, then they are also in equilibrium with each other; if the systems are in thermal equilibrium, no heat flow will take place

Law of Conservation of Energy

Energy cannot be created or destroyed. It can be transferred from one location to another and be converted to and from other forms of energy

First Law of Thermodynamics

Total change in internal energy (∆E) is the sum of the energy transferred as heat (Q) and/or work (W)

Heat (Q)

energy transferred from a hotter object to a colder one (temperature difference)

Work (W)

energy transferred as a a result of macroscopic forces

+Q

heat absorbed by the system (from the surroundings)

-Q

heat released by the system (to the surroundings)

+W

work done on the system (by the surroundings)

-W

work done by the system (on the surrounding)

pressure-volume work

work done by fluids in a thermodynamic system; occurs whenever there is a change in volume and external pressure remains constant

W = -P∆V

pressure-volume work

heat transfer

total heat lost by the hot body is equal to the total heat gained by the cold body; process of thermal energy exchange due to temperature differences

Q = mCp∆T = mCp(T2-T1)

sensible heat

Q=mLf, Q=mLv

latent heat

Lf

latent heat of fusion/solidifaction

+Lf

fusion (solid to liquid)

-Lf

solidification (liquid to soid)

Lv

latent heat of vaporation/condensation

+Lv

vaporization (liquid to vapor)

-Lv

condensation (vapor to liquid)