Unit 9H Lesson 5 Endothermic and Exothermic Reactions Objective: to learn the difference between endothermic and exothermic reactions

Endothermic Reactions Endothermic reactions are reactions which take energy in from their surroundings. If a substance is undergoing an endothermic reaction would it’s surroundings get warmer or colder? It’s surroundings get colder. Endothermic reactions occur when the bonds of a substance are being broken.

Useful Endothermic Reactions When things dissolve they are undergoing an endothermic reaction. Cooking is an endothermic reaction. The food takes in the heat provided by the cooker. The chemicals of the food undergo a chemical reaction which makes them easier to digest. Cold packs for sports injuries rely on endothermic reactions. See figure 2 page 100. When you twist or shake the pack the chemicals in the pack start reacting. Because they undergo an endothermic reaction they take heat in from their surroundings. This makes the pack cold.

Exothermic Reactions Exothermic reactions give off heat. They occur when chemical bonds are formed. If substances are undergoing exothermic reactions will their surroundings get hotter or colder? The will get hotter.

Useful Exothermic Reactions Combustion: all combustion reactions give off heat. Neutralization reactions are exothermic. Hot Pad hand warmers (see figure 1 page 100) When the hand warmer is shaken they chemicals inside undergo an exothermic reaction This releases the heat which helps to warm up your hand. Self heating coffee cans. When the tab is popped chemicals mix together and an exothermic reaction occurs. This releases heat which warms up your coffee. The chemicals are kept separate from the coffee

Work to Do Complete questions 1-6 page 101. Homework Complete H/W sheet 8.3 Define the following keywords: Endothermic, exothermic,