1. Thermochemistry is the study of heat change in chemical reactions. Chapter 5 Energy & Rates of Reaction Unit 3

2. Chapter 5 Key Concepts: After completing this chapter you will be able to….. compare the energy changes of different substances, perform calorimetry calculations, and describe the relationship between reactions using enthalpy terms. represent thermochemical equations using different methods, and determine whether a reaction is exothermic or endothermic calculate and use bond energies to estimate the enthalpy change of a reaction. define and solve problems using Hess’s law. write formation reactions and calculate enthalpy changes using standard enthalpy of formation values. describe current and future energy sources and explain their advantages and disadvantages

3. 5.1: Energy: is the capacity to do work Thermal energy is the energy associated with the random motion of atoms and molecules Chemical energy is the energy stored within the bonds of chemical substances Nuclear energy is the energy stored within the collection of neutrons and protons in the atom Electrical energy is the energy associated with the flow of electrons Potential energy is the energy available by virtue of an object’s position 5.1

4. Heat is the transfer of thermal energy between two bodies that are at different temperatures. Energy Changes in Chemical Reactions Temperature is a measure of the thermal energy. Temperature = Thermal Energy 90 0 C 40 0 C greater thermal energy 5.1 thermal energy: the total quantity of kinetic and potential energy in a substance

5. Law of Conservation of EnergyLaw of Conservation of Energy: Energy cannot be created or destroyed The system is the specific part of the universe that is of interest in the study. open mass & energyExchange: closed energy isolated nothing SYSTEM SURROUNDINGS 5.1

6. Exothermic process is any process that gives off heat – transfers thermal energy from the system to the surroundings. Endothermic process is any process in which heat has to be supplied to the system from the surroundings. 2H 2 (g) + O 2 (g) 2H 2 O (l) + energy H 2 O (g) H 2 O (l) + energy energy + 2HgO (s) 2Hg (l) + O 2 (g) 5.1 energy + H 2 O (s) H 2 O (l)

7. Nuclear Energy All nuclear reactions are exothermic. Per unit of mass, nuclear reactions release much more energy than exothermic chemical reactions. Two main types of Reactions: Fusion and Fission A fusion reaction occurs when nuclei of small atomic mass combine to form larger molecule. 2 1 H + 3 1 H → 4 2 He + 1 0 n In Fission, large nuclei with high atomic mass are split to smaller, lighter mass by collision with a neutron: 235 92 U + 1 0 n → 92 36 Kr + 141 56 Ba + 3 1 0 n + 1.9 x 10 10 kJ/mol See P. 290 Table 1 5.1

8. Chapter 5.1 Assignment Read page# 286 -291. Answer Questions 1 to 7 (page 291) 5.1

9. The specific heat (c) of a substance is the amount of heat (q) required to raise the temperature of one gram of the substance by one degree Celsius. 5.2: Calorimetry and Enthalpy The heat capacity (C) of a substance is the amount of heat (q) required to raise the temperature of a given quantity (m) of the substance by one degree Celsius. C = mc Heat (q) absorbed or released: q = mc  t q = C  t  t = t final - t initial 5.2

10. Calorimetry: the measurement of heat into or out of a system for chemical and physical processes. the heat released = the heat absorbed The device used to measure the absorption or release of heat in chemical or physical processes is called a “Calorimeter” 5.2

11. Enthalpy (H): Total amount of thermal energy in a substance: Enthalpy Change (∆H) : Energy changes in Physical and Chemical Reactions The enthalpy change of the chemical system is equal to the flow of thermal energy in and out of the system, ∆H surrounding = |q system | ∆H surrounding > 0, Endothermic reaction ∆H surrounding < 0, Exothermic reaction 5.2