Thermochemistry

• Do Now – Check and edit prelabs

• Objective – Thermochemistry • Exothermic, endothermic, calorie, joule, heat

capacity, and specific heat

• Homework – Pg 510 # 9-11

Energy Transformations

Energy is the capacity to do work or supply heat

Energy has no mass or volume

Energy Transformations

Energy is the capacity to do work or supply heat

Energy has no mass or volume

Thermochemistry = study of energy changes that occur during chemical reactions

Heat (q) always flow from warmer to cooler

Exothermic and Endothermic Processes

System and Surroundings

Law of conservation of energy

Exothermic and Endothermic Processes

System and Surroundings

Law of conservation of energy

Exothermic and Endothermic Processes

Endothermic Reactions – System absorbs energy from surroundings

Exothermic Reactions- System gives off energy to the surroundings

Units of Measuring Heat Flow

calorie = amount of heat it takes to raise the temp of 1 g of water 1 °C

Units of Measuring Heat Flow

calorie = amount of heat it takes to raise the temp of 1 g of water 1 °C

1 Calorie = 1 Kilocalorie = 1000 calories

Units of Measuring Heat Flow

calorie = amount of heat it takes to raise the temp of 1 g of water 1 °C

1 Calorie = 1 Kilocalorie = 1000 calories

Joule (J) is the SI unit for measuring energy1 J = 0.2390 cal 4.184 J = 1 cal

Heat Capacity and Specific Heat (C)

Heat Capacity = amount of heat needed to increase the temp of an object 1 °C

Heat Capacity and Specific Heat (C)

Heat Capacity = amount of heat needed to increase the temp of an object 1 °C

Specific Heat = amount of heat needed to increase the temp of 1 gram of a material 1 °C

Heat Capacity and Specific Heat (C)

C = q = heat (Joules or calories)__ m x ∆T mass(g) x change in temp (°C )

Calculating the Specific Heat of a Metal

C = q = heat (Joules or calories)__ m x ∆T mass(g) x change in temp (°C ) Sample Problem 17.1 pg 510

The temperature of a 95.4 gram piece of copper increases from 25.0 °C to 48.0 °C when the copper absorbs 849 J of heat. What is the specific heat of copper?

Calculating the Specific Heat of a Metal

C = q = heat (Joules or calories)__ m x ∆T mass(g) x change in temp (°C ) Sample Problem 17.1 pg 510

The temperature of a 95.4 gram piece of copper increases from 25.0 °C to 48.0 °C when the copper absorbs 849 J of heat. What is the specific heat of copper?

Enthalpy

EnthalpyHeat content of a system at constant pressure

Enthalpy

qsys

= ∆H = -qsurr

= -m x C X ∆T

17.1

9. 1.76 x 103 cal 1.76 kcal 7.36 x 103 J 7.36 kJ

10. 2.36 x 10-1 J/(g*°C)

11. 2.8 x 102 kJ

17.2

18. 2Mg(s) + O2(g) → 2MgO(s) + 1204 kJ or

2Mg(s) + O2(g) → 2MgO(s) ∆H= -1204 kJ

19. 3.72 x 102 kJ

20. Heat of combustion is the heat of reaction for the complete burning of one mole of a substance.