Chemistry 141

• More Practice !!


  aq + H2 (g) → MnO2 + 4 HCl → MnCl2 + Cl2 + 2 H2O
• Chapter 10 - Thermochemistry

  2 NH4NO3 (s) → 2 N2 (g) + O2 (g) + 4 H2O (g)
• Conversion Between Energy Units

  Conversion between different units of energy
• First Law of Thermodynamics


  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