Thermochemistry (UNIT 2) Grade 12 Chemistry SCH4U0

What is THERMOCHEMISTRY? THERMOCHEMISTRY is the study of the energy changes that accompany physical or chemical changes in matter. THERMOCHEMISTRY is the study of the energy changes that accompany physical or chemical changes in matter.

Energy Transformations

Heat vs. Temperature Heat (q) is the amount of energy transferred between substances (Units: Joules (J), kJ, kJ/mol) Temperature (T) is the measure of the average kinetic energy (energy of motion) of the particles in a sample of matter (Units: o C, o K, o F)

Heat and Energy Changes What are the products when methane combusts in air? CH 4 + 2O 2  CO 2 + 2H 2 O + energy thermal energy (heat) Energy that is released from this CHEMICAL SYSTEM to the SURROUNDINGS is called thermal energy (heat). Since the molecules have greater kinetic energy, temp. of surroundings increases

System and Surroundings system The system is a well-defined part of the universe singled out for study. surroundings The surroundings is the remainder of the universe. closed system In a closed system energy, but not matter, can be exchanged with the surroundings. open system In an open system, both energy and matter can flow into our out of the system. isolated system In an isolated system (ideal system) neither matter nor energy can move in or out.

Exothermic and Endothermic Processes Heat (q) is a form of energy transfer. Units: 1 calorie (cal) = J q > 0 Heat is transferred from surrounding to system. Process is endothermic. q < 0 Heat is transferred from system to surroundings. Process is exothermic. System Surroundings qq

A basic calorimeter ) Endothermic = absorbing energy Law of conservation of energy = release and absorption of energy must be equal Surroundings everything else Exothermic = releasing energy System with can as boundary

Heat and Temperature Change How is heat transferred related to the change in temperature of a system with mass m? q = specific heat (c)  m   T The specific heat (c) of a substance is the amount of heat required to raise the temperature of 1 gram by 1   C. Al 0.90 J/g  C H 2 O 4.18 J/g  C

Example Question 1

Let's try this question now If grams of iron at 95.0 °C, is placed in an insulated container containing grams of water at 25.0 °C, and both are allowed to come to the same temperature, what will that temperature be? The specific heat of water is 4.18 J/g °C and the specific heat of iron is J/g °C)

Energy and Enthalpy

HEATHEATHEATHEAT

HEATHEATHEATHEAT

Molar Enthalpy

Types of Molar Enthalpies

Enthalpies of Reaction H is an extensive property, so  H depends on the amounts of reactants and products. What is  H for the combustion of 11.0 g of CH 4 in excess oxygen? CH 4 (g) + 2 O 2 (g)  CO 2 (g) + 2 H 2 O(g)  H = kJ = -550 kJ 11.0 g CH 4

Example Question (p.309)

Calorimetry of Physical and Chemical Changes

Homework Questions