Chem 14B - Thermodynamics Flashcards
(44 cards)
If no other energy is transferring:
∆U = w
Formula for Volume change, no heat change:
w = P∆V or w = -P∆V (expansion, work)
If energy is transferred ONLY as heat:
∆U = q
Exothermic
Releases heat to surroundings, ∆H < 0
Endothermic
Absorbs heat from surroundings, ∆H > 0
If heat capacity is known:
q = C∆T; C = heat capacity
∆U = q + w
U = internal energy. This formula is always true.
At constant volume, heat transfer is interpreted as:
∆U;
q = ∆U;
U = total energy in a system
At constant pressure, heat transfer is interpreted as:
∆H;
q = ∆H;
H = tracks losses & gains of energy as expansion or compression work during heat at constant pressure
H = U + PV -> PV = nRT
∆H = ∆U + ∆n(gas)RT
Isothermal:
No change in temperature. ∆T = 0
∆U = 0
∆U = 0 = q + w; q = -w or -q = w
“Compresses reversibly”
Constant Pressure
“in a bomb calorimeter”
Constant Volume
Bomb Calorimeter Equation
q(cal) = C(cal)∆T
Equation for reversible, isothermal expansion/compression:
w = -nRT ln (v2/v1)
Equation for when system expands/compresses with constant external pressure:
w = -P∆V
Equation if you know mass, specific heat and temperature change:
q = mC(s)∆T
Equation if you know moles, specific heat, and temperature change:
q = nC(m)∆T
Equation for melting (fusion) point phase change:
q(fus) = n∆H(fus)
Equation for freezing point phase change:
q(freez) = -n∆H(fus) -> opposite of fusion
Equation for vaporization phase change:
q(vap) = n∆H(vap)
Equation for condensation phase change:
q(cond) = -n∆H(vap) -> opposite of vaporization
Molar Heat Capacity: Constant Volume C(v,m), Atom
3/2R
Molar Heat Capacity: Constant Volume C(v,m), Linear Molecules
5/2R
