Reaction Energy and Reaction
Kinetics
Thermochemistry
ThermochemistryObjectives:
1. Define heat and temperature.
2. Perform specific heat calculations.
Temperature and Heat
Temperature – measure of the average kinetic energy of the particles of a substance.
What are the units? oC, K
Heat – the flow of energy from one substance to another.
What are the units?
Joules, calories, Calories, kJ, kcal
1 cal = 4.184 J
Specific HeatSpecific Heat (C): the amount
of energy needed to raise the temperature of 1 gram of a substance by 1 degree celcius
For water:
C = 4.184 J/goC
C = 1 cal/g0C
Specific Heat
TCmq q = heat (joule or cal)
m= mass (grams)
C = specific heat (J/g*C) or (cal/g*C)
ΔT= change in temperature (oC)
Specific Heat Problems1. Determine the specific heat of a material if a 35 g
sample absorbed 48 J as it was heated from 293K to 313K.
2. If 980 kJ of energy are added to 6.2 L of water at 18oC, what will the final temperature be?
Heat of ReactionEnthalpy (H) – heat content of a system
Enthalpy change (ΔH) – amount of energy absorbed or lost by a system during a process at constant pressure.
ΔH = Hproducts- Hreactants
Heat of Reaction
Heat of Reaction
Combustion of propane
C3H8 (g) + 5 O2(g) 3 CO2 (g) + 4 H2O(g) + 2043 kJ
ΔH = -2043 kJ (exothermic)
Formation of synthesis gas
C(s) + H2O(g) +113kJ CO(g) + H2(g)
ΔH = +113 kJ (endothermic)
Sample Problems1. How much heat will be released when 6.44 g of sulfur
reacts with excess O2 according to the following equation?
2 S + 3 O2 2 SO3 ΔH = -791.4 kJ
2. How much heat is transferred when 9.22 g of glucose (C6H12O6) in your body reacts with O2 according to the following equation?
C6H12O6 (s) + 6 O2(g) 6 CO2 (g) + 6 H2O(l) ΔH= -2803 kJ
Heat of FormationMolar Heat of Formation (∆Hf
0 ) – energy change that occurs when 1 mole of a compound forms from the combination of its elements.
H2 (g) + 1/2 O2 (g) H2O(l) ∆Hf
0 = -285.8 kJ/mol
C(s) + O2 (g) CO2 (g) ∆Hf0 = -393.5 kJ/mol
Stability and Heat of FormationAl2O3 (s) -1676.0 kJ/mol
CaCO3(s) -1206.92 kJ/mol
NO(g) 90.29 kJ/mol
O3(g) 142.7 kJ/mol
• Stability goes with a high negative heat of formation.
Heat of CombustionHeat of Combustion (∆Hc
0) –energy released with the combustion of one mole of a substance.
C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O(l)
∆Hc0 = -2219.2
kJ/mol