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