Thermodynamics is the study of energy and its interconversions. The total amount of energy in the universe is constant; it is conserved.
System
The area or location under study
Surroundings
Area or location outside the system
Universe
System + surroundings
Endothermic
Heat transfers from surroundings to the system
Exothermic
Heat transfers from the system to the surroundings
State Function
Regardless of the trail, when you reach the top, you will be 10,000 ft above the base
ΔE and ΔH
Are state functions
q and w
Are not state functions
Energy Exchange
E = w + q
Work
Transfer of energy by motion (macroscopic objects)
Heat
Transfer of thermal energy (vibration of atoms/molecules)
Heat
The exchange of thermal energy between a system and its surroundings
Temperature
The measure of thermal energy in a system
Specific Heat Capacity
Measure of a substance's intrinsic ability to absorb heat. The specific heat capacity is the amount of heat energy required to raise the temperature of one gram of a substance 1 °C.
Example
A Cu block of unknown mass has an initial temperature of 65.4°C. It is immersed in a beaker of water (m=95.7 g) at 22.7°C. The two substances reach thermal equilibrium at 24.2°C. What is the mass of the copper? (Cs,Cu = 0.385 J/g·K)
Pressure–Volume Work
PV work is work caused by a volume change against an external pressure. w = –PΔV. Units of w (atm·L)
Bomb Calorimeter
w = –PΔV because ΔV=0 (constant volume) so w=0. ΔErxn = wrxn + qrxn. ΔErxn = qrxn (change in energy equals heat of reaction). qcal = -qrxn. qcal = Ccal x ΔT
Heat
The exchange of thermal energy between a system and its surroundings
Temperature
The measure of thermal energy in a system
Thermal properties
Hot
Cold
Net heat transfer
Specific Heat Capacity
Measure of a substance's intrinsic ability to absorb heat
The amount of heat energy required to raise the temperature of one gram of a substance 1°C
The specific heat of copper is 0.385 J/(g·°C)
Calculating heat changes
1. Heat (J)
2. Specific Heat Capacity
3. Change in temperature (°C)
4. Mass (g)
PV work
Work caused by a volume change against an external pressure
w = -PΔV
Bomb Calorimeter
w = -PΔV because ΔV=0 (constant volume), so w=0
ΔE_rxn = q_cal = -q_rxn
q_cal = C_cal x ΔT
Enthalpy (ΔH)
Heat of Reaction
ΔH is the amount of heat absorbed or released by a reaction at constant pressure
If ΔH is positive: endothermic
If ΔH is negative: exothermic
Constant Pressure Calorimetry
q_cal = -q_rxn
q_cal = mass_sol x C_s, sol x ΔT
ΔH = q_cal (At constant pressure)
Comparing ΔH with ΔE
If moles of gas reactants = moles of gas products, then ΔH = ΔE
Otherwise, ΔH = ΔE + PΔV
Hess's Law
∆Erxn
Change in internal energy of a reaction
∆V=0
Therefore w=0
Bomb Calorimeter
Used for solid reactants
Enthalpy (∆H)
Heat of Reaction
∆H
Amount of heat absorbed or released by a reaction at constant pressure
Constant Pressure Calorimetry
qcal = -qrxn
qcal = mass sol x Cs, sol x ∆T
Example
50.0 g 0.200 M NaCl(aq) at 24.1 °C is added to 100.0 g of 0.100 M AgNO3(aq) at 24.1 °C in a calorimeter, the temperature increases to 25.2 °C as AgCl(s) forms
Calculate the approximate amount of heat in joules produced