Objective  To understand the forms of energy  kinetic, potential, chemical and thermal  To understand the law of conservation of energy and how energy is measured  To understand the process of heat transfer

Thermochemistry – Heat and Chemical Change The flow of energy

 Thermochemistry is concerned with the heat changes that occur during chemical reactions.

Four Types of Energy 1. Kinetic Energy – energy of motion  Depends on the mass and speed of the object  Example: car vs. bicycle 2. Potential Energy – stored energy from the attraction and repulsion an object experiences  Based on gravity or electrostatic attractions  Example: bicycle at the top of a hill 3. Chemical Energy – potential energy stored in the bonds of atoms in a chemical  Released during chemical reactions 4. Thermal Energy – kinetic energy of a substance related to the temperature of that substance  Caused by vibrating or moving molecules  NOT the same thing as heat!

Types of Energy  Determine which type of energy is being described:  Gasoline –  Burning Wood –  Water at the top of a waterfall –  A man running -

Types of Energy  Determine which type of energy is being described:  Gasoline – chemical energy  Burning Wood – thermal energy  Water at the top of a waterfall – potential energy  A man running - kinetic energy

The Flow of Energy  Energy is the capacity for doing work.  The law of conservation of energy says: Law of Conservation of Energy Energy is never created or destroyed in any chemical or physical change. Law of Conservation of Energy Energy is never created or destroyed in any chemical or physical change. You can ONLY change energy from one form to another…

Heat (Q)  Heat (Q) is energy that transfers from one object to another because of a temperature difference between them.  Heat cannot be detected by instruments or our senses, only the changes that are caused by heat can be detected

What causes heat to transfer from an object? A. Only objects at equilibrium can transfer heat B. A difference in temperature between objects C. A difference in mass between objects

Heat (Q)  Heat (Q) always flows from a warmer object to a cooler object until the objects are at equilibrium.  Which direction is heat flowing in each case? Room ARoom B

Exothermic and Endothermic processes  Chemical Potential Energy is energy stored in chemical substances  some examples: gasoline, AA battery, firefly

Exothermic and Endothermic processes  All chemical reactions either absorb or release heat to their surroundings  The law of conservation of energy is always true  We can account for all the energy in a chemical reaction as either work, stored energy, or heat.

Exothermic and Endothermic processes  A process that releases heat to the surroundings is called an exothermic process.  A process that absorbs heat from the surroundings is called an endothermic process.

Energy Diagrams – complete the diagrams in your notes  Energy Diagrams show the change in potential energy in the reactants and products of a reaction.  Energy Diagrams can be used to determine if a chemical reaction is exothermic or endothermic If potential energy in the reactants is released as heat, the reaction is exothermic and feels hot. If potential energy in the products is increased (absorbed) the reaction is endothermic and feels cold.

Energy Diagrams – complete the diagrams in your notes  Energy Diagrams show the change in potential energy in the reactants and products of a reaction.  Energy Diagrams can be used to determine if a chemical reaction is exothermic or endothermic If potential energy in the reactants is released as heat, the reaction is exothermic and feels hot. If potential energy in the products is increased (absorbed) the reaction is endothermic and feels cold.

Example:  Nitrogen gas reacts with hydrogen gas to form ammonia gas according to the energy diagram below:  Does this energy diagram represent an endothermic or exothermic reaction?

Example: Nitrogen gas reacts with hydrogen gas to form ammonia gas according to the energy diagram below: This energy diagram represents a(n) ______ reaction. A. Exothermic B. Endothermic C. Ectoplasmic D. Cannot be determined

Example:  Does the energy diagram below represent an endothermic or exothermic reaction?

The energy diagram below represents a(n) ______ reaction. A. exothermic B. endothermic C. echolothermic D. cannot be determined [Default] [MC Any] [MC All]

Measuring Heat (Q)  Heat is measured in calories, Calories or joules.  Whether you are breaking down sugar in your body to create heat or burning sugar in a fire to create heat, the chemical reaction produces the same number of calories.

Measuring Heat (Q) What is a calorie?  1 calorie ( cal ) = the quantity of heat needed to raise the temperature of 1 g of pure water 1 o C  the food C alorie is spelled ‘CAPITOL C’  1 C alorie = 1 kilocalorie = 1000 calories  We will use the SI unit for energy, the Joule 1 calorie = J

Quiz Question #1: How many joules of energy does it take to raise the temperature of 1 g of pure water by 1 o C? _______ A. 1 joule B joule C joule D joule

Measuring Heat (Q) What is a calorie?  1 calorie ( cal ) = the quantity of heat needed to raise the temperature of 1 g of pure water 1 o C  the food C alorie is spelled ‘CAPITOL C’  1 C alorie = 1 kilocalorie = 1000 calories  We will use the SI unit for energy, the Joule 1 calorie = J

Key terms and concepts to know  Thermochemistry  Energy and its forms  Heat (Q) and how does it flow  Chemical Potential Energy  Law of Conservation of Energy  Exothermic reaction  Endothermic reaction  Energy Diagram: recognize endothermic vs. exothermic  calorie  Calorie  joule