Thermochemistry

11.1 Heat Symbol: q Energy that transfers from one object to another NOT TEMPERATURE!!!!!! Observable temperature is caused by heat

Energy The capacity to do work Law of Conservation of Energy “1 st Law of Thermodynamics” Energy is neither created nor destroyed!!!

Exo- and Endo- Thermic Processes

Describing the direction of heat flow in terms of the system that we are considering.

How is heat measured??? calories Joules 1 calorie: quantity of heat needed to raise the temperature of 1 gram of water by 1°C.

Heat capacity The amount of heat needed to increase the temperature of an object by 1°C. Specific Heat capacity The amount of heat needed to increase the temperature of 1 gram of an object by 1°C.

Specific Heat equation C = q m· Δ T C : Specific heat q= heat (Joules or calories) m = mass (grams) Δ T = Temperature change (°C)

Practice Problem What is the specific heat of 32 g of a metal that releases 500 Joules of heat when cooling from 100 °C to 28 °C?

Practice Problem What is the specific heat of 32 g of a metal that releases 500 Joules of heat when cooling from 100 °C to 28 °C? 32 g = Mass 500 Joules = q 100° – 28° = 72° = Δ T C = q m· Δ T

Practice Problem What is the specific heat of 32 g of a metal that releases 500 Joules of heat when cooling from 100 °C to 28 °C? 32 g = Mass 500 Joules = q 100° – 28° = 72° = Δ T C = q= 500 J= m· Δ T (32 g) (72° C )

Practice Problem What amount of heat is required to raise the temperature of 20 g of a substance from 20 °C to 75°C, when it has a specific heat capacity of calories/g°C

Practice Problem What amount of heat is required to raise the temperature of 20 g of a substance from 20 °C to 75°C, when it has a specific heat capacity of calories/g°C 20 g = mass 75°-20° = 55° = Δ T calories/g·°C = C

Practice Problem What amount of heat is required to raise the temperature of 20 g of a substance from 20 °C to 75°C, when it has a specific heat capacity of calories/g°C 20 g = mass 75°-20° = 55° = Δ T calories/g·°C = C q= mC  T =

Practice Problem What amount of heat is required to raise the temperature of 20 g of a substance from 20 °C to 75°C, when it has a specific heat capacity of calories/g°C 20 g = mass 75°-20° = 55° = Δ T calories/g·°C = C q= mC  T = (20g)(0.635 cal/g °C) (55 °C) = cal

Calorimetry A technique to measure heat change for chemical and physical processes. The heat released by the system is absorbed by the surroundings.

Enthalpy Δ H Heat content q = Δ H From our previous equation C = q m· Δ T Δ H = q = m · C · Δ T

Thermochemical Equation C + 2S kJ  CS 2 When heat is a reactant, it is absorbed by the system. CuO + Cu  Cu 2 O kJ When heat is a product, it is released by the system.

Thermochemical Equation C + 2S kJ  CS 2 When heat is a reactant, it is absorbed by the system. What is the sign of Δ H? CuO + Cu  Cu 2 O kJ When heat is a product, it is released by the system. What is the sign of Δ H?

Thermochemical Equation C + 2S kJ  CS 2 When heat is a reactant, it is absorbed by the system. What is the sign of Δ H? kJ ENDOTHERMIC CuO + Cu  Cu 2 O kJ When heat is a product, it is released by the system. What is the sign of Δ H? – 11.3 kJ EXOTHERMIC

Problem solving with Thermochemical Equations C + 2S kJ  CS 2 Calculate the amount of heat required to form 3 mol of CS 2.

Problem solving with Thermochemical Equations C + 2S kJ  CS 2 Calculate the amount of heat required to form 3 mol of CS 2. From the given equation we know that 89.3 kJ will produce 1 mol of CS 2 So, our conversion factor will be 89.3 kJ 1 mol CS 2

Problem solving with Thermochemical Equations C + 2S kJ  CS 2 Calculate the amount of heat required to form 3 mol of CS 2. 3 mol CS kJ = kJ 1 mol CS 2

CuO + Cu  Cu 2 O kJ How many kilojoules of heat are released when 2.3 mol of CuO reacts with excess Cu to form Cu 2 O?

CuO + Cu  Cu 2 O kJ How many kilojoules of heat are released when 2.3 mol of CuO reacts with excess Cu to form Cu 2 O? 2.3 mol CuO 11.3 kJ = kJ 1 mol CuO

CH O 2  CO H 2 O kJ How much heat is produced when 4.7 mol of oxygen gas (O 2 ) reacts with methane to form carbon dioxide and water?

CH O 2  CO H 2 O kJ How much heat is produced when 4.7 mol of oxygen gas (O 2 ) reacts with methane to form carbon dioxide and water? 4.7 mol O kJ = kJ 2 mol O 2

THE END!!!