Reaction Energy and Reaction Kinetics Thermochemistry

Objectives: 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? o C, K Heat – the flow of energy from one substance to another. What are the units? Joules, calories, Calories, kJ, kcal 1 cal = J

Specific Heat Specific Heat (C): the amount of energy needed to raise the temperature of 1 gram of a substance by 1 degree celcius For water: C = J/g o C C = 1 cal/g 0 C

Specific Heat q = heat (joule or cal) m= mass (grams) C = specific heat (J/g*C) or (cal/g*C) ΔT= change in temperature ( o C)

Specific Heat Problems 1.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 18 o C, what will the final temperature be?

Heat of Reaction Enthalpy (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 = H products - H reactants

Heat of Reaction

Combustion of propane C 3 H 8 (g) + 5 O 2(g)  3 CO 2 (g) + 4 H 2 O (g) kJ ΔH = kJ (exothermic) Formation of synthesis gas C (s) + H 2 O (g) +113kJ  CO (g) + H 2(g) ΔH = +113 kJ (endothermic)

Sample Problems 1.How much heat will be released when 6.44 g of sulfur reacts with excess O 2 according to the following equation? 2 S + 3 O 2  2 SO 3 ΔH = kJ 2.How much heat is transferred when 9.22 g of glucose (C 6 H 12 O 6 ) in your body reacts with O 2 according to the following equation? C 6 H 12 O 6 (s) + 6 O 2(g)  6 CO 2 (g) + 6 H 2 O (l) ΔH= kJ

Heat of Formation Molar Heat of Formation (∆H f 0 ) – energy change that occurs when 1 mole of a compound forms from the combination of its elements. H 2 (g) + 1 / 2 O 2 (g)  H 2 O (l) ∆H f 0 = kJ/mol C (s) + O 2 (g)  CO 2 (g) ∆H f 0 = kJ/mol

Stability and Heat of Formation Al 2 O 3 (s) kJ/mol CaCO 3(s) kJ/mol NO (g) kJ/mol O 3(g) kJ/mol Stability goes with a high negative heat of formation.

Heat of Combustion Heat of Combustion (∆H c 0 ) –energy released with the combustion of one mole of a substance. C 3 H 8(g) + 5 O 2(g)  3 CO 2(g) + 4 H 2 O (l) ∆H c 0 = kJ/mol