Brain Break

What are we doing Today? Ch. 3 (EST) Test Endothermic & Exothermic Rxns Lab 31 (EST) on Wednesday Ch. 4 (ST) Test on December 3 Work on PreLab for Wednesday

Dates of Tests/Labs Lab 31 Endothermic/Exothermic Wed, Nov 26 (Finish PreLab 1 st page for class) Ch. 4 ST Test, Wednesday, December 3 Tutorial Monday, December 1 after school

Endothermic and Exothermic Reactions Ch.4 (EST)

Exothermic Reactions What does it mean? It is a chemical change that releases energy

Exothermic Reactions What are they? A reaction is classified as exothermic when it is a chemical reaction that releases energy in the form of heat, light or sound.

Endothermic Reactions What does it mean? A chemical change that absorbs energy

Endothermic Reactions What are they ? A reaction is considered to be endothermic when it absorbs heat light or sound. The heat light or sound leave the surroundings and enters the system.

Exothermic and Endothermic Reactions How can you tell the difference? When an exothermic reaction occurs it releases energy; usually in the form of heat or light. These reactions can be everyday reactions like the combustion of fuel in your car that makes it work. Endothermic reactions absorb the energy instead of releasing it. A simple example of an endothermic reaction would be melting an ice cube. The cube absorbs the heat on the outside warming it causing it to melt.

Table 4.12 & 4.13 (p.115)

2H 2 + O 2  2H 2 O Calculate the amount of energy involved in breaking or forming bonds H 2 is a single bond O 2 is a double bond H 2 O is a single bond Energy absorbed by the reactants: 864KJ + 494KJ = 1358 KJ Energy released by the products: 1840 KJ Reaction Energy: 1358 KJ – 1840 KJ = -484 KJ Is it an Endothermic Reaction or an Exothermic Reaction? Negative and therefore releases more energy then it absorbs so it is Exothermic

2H 2 0  2H 2 + O 2 Hints: H 2 0 is a single bond H 2 is a single bond Use p.115 O 2 is a double bond tables 4.12 & 4.13 Is it an Endothermic or Exothermic Rxn ? Energy absorbed by the reactants: 4 x 464 KJ = 1856 KJ Energy released by the products: (2 x 435 KJ) + (498 KJ) = 1368 KJ Released Energy: 1856 KJ – 1368 KJ = +488 KJ Positive energy, therefore absorbs energy and is Endothermic

Is it an Exothermic or Endothermic Reaction ? Negative Reaction Energy And is releasing energy so is: Exothermic

Classwork to do: -Complete question 14 on p.133 of textbook -Read over Lab 31 and complete the first page (prelab) -Study for Ch.4 (ST) Test