Mr Quinn Ms Tom February 24 2014 Aim

Mr. Quinn & Ms. Tom February 24, 2014 Aim: How do we determine where energy goes in a chemical reaction? Do Now: List one reaction that increases the surrounding temperature, and one reaction the decreases the surrounding temperature. • •

The Laws of Thermodynamics 1. Energy cannot be created or destroyed 2. The disorder of a system increases over time

Two Types of Reactions Exothermic Reactions Endothermic Reactions • Temperature increases • Temperature decreases • Energy is released • Energy is absorbed • Heat is a product • Heat is a reactant

Example 1

Example 1 • Did the temperature of the surroundings increase or decrease? • INCREASE • Is the reaction pictured exothermic or endothermic? • EXOTHERMIC • Provide one justification for your answer to the previous question. • TEMPERATURE INCREASED AND THERE WAS A FIRE • Where was the energy released to? • THE AIR • Would you predict that the products have a higher or lower energy than the reactants?

Example 2

Example 2 • Did the temperature of the surroundings increase or decrease? • DECREASE • Is the reaction pictured exothermic or endothermic? • ENDOTHERMIC • Provide one justification for your answer to the previous question. • TEMPERATURE DECREASCED • Where was the energy absorbed from? • THE WATER • Would you predict that the products have a higher or lower energy than the reactants?

Let’s Try It Out! Melting ice causes the temperature of the air When water vapor forms snow (deposition), to DECREASE. Is the process of melting the temperature of the air INCREASES. Is exothermic or endothermic? Why? deposition exothermic or endothermic? Why?

Let’s Try It Out! Dissolving table salt in water is endothermic. Burning Mg creates a hot white flame. Is this What do you expect to happen to the process exothermic or endothermic? Explain. temperature of the water?

Let’s Try It Out! A process is exothermic. Is energy a product or reactant? A process leaves products with less energy than the reactants. Is it exothermic or endothermic?

Your Turn!