April 22, 2013 AGENDA: 1 – Bellringer & Part’n Log 2 – CN: Hess’s Law & Reaction Coordinate Diagrams 3 – Practice Problems 4 – Work time Today’s Goal: Students will be able to use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams. Homework 1. Hess’s Law HW 2. Week 31 make-up QUIZ must be done by Friday. 3. Week 31 work is due by Friday.

Monday, April 22 Objective: Students will be able to use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams. Bell Ringer: Describe each of the following situations as either exothermic or endothermic reactions: 1. Temperature of the surroundings decreases. 2. Temperature of the surroundings increases. 5 minutes!

4 MINUTES REMAINING…

Monday, April 22 Objective: Students will be able to use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams. Bell Ringer: Describe each of the following situations as either exothermic or endothermic reactions: 1. Temperature of the surroundings decreases. 2. Temperature of the surroundings increases. 4 minutes!

3 MINUTES REMAINING…

Monday, April 22 Objective: Students will be able to use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams. Bell Ringer: Describe each of the following situations as either exothermic or endothermic reactions: 1. Temperature of the surroundings decreases. 2. Temperature of the surroundings increases. 3 minutes!

2 MINUTES REMAINING…

Monday, April 22 Objective: Students will be able to use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams. Bell Ringer: Describe each of the following situations as either exothermic or endothermic reactions: 1. Temperature of the surroundings decreases. 2. Temperature of the surroundings increases. 2 minutes!

1 MINUTE REMAINING…

Monday, April 22 Objective: Students will be able to use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams. Bell Ringer: Describe each of the following situations as either exothermic or endothermic reactions: 1. Temperature of the surroundings decreases. 2. Temperature of the surroundings increases. 1 minute!!!

30 seconds Remaining…

Monday, April 22 Objective: Students will be able to use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams. Bell Ringer: Describe each of the following situations as either exothermic or endothermic reactions: 1. Temperature of the surroundings decreases. 2. Temperature of the surroundings increases. 30 seconds!!!

10 Seconds Remaining…

BELL- RINGER TIME IS UP!

April 22, 2013 AGENDA: 1 – Bellringer & Part’n Log 2 – CN: Hess’s Law & Reaction Coordinate Diagrams 3 – Practice Problems 4 – Work time Today’s Goal: Students will be able to use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams. Homework 1. Hess’s Law HW 2. Week 31 make-up QUIZ must be done by Friday. 3. Week 31 work is due by Friday.

Monday, April 22 Objective: Students will be able to use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams. Bell Ringer: Describe each of the following situations as either exothermic or endothermic reactions: 1. Temperature of the surroundings decreases. 2. Temperature of the surroundings increases. REVIEW

Notes Topic: Hess’s Law & Reaction Coordinate Diagrams Date: 4/22/2013

Hess’s Law Germain Hess ( ) was a Swiss-born Russian chemist and physician. ∆H = H Products – H reactants ∆H = H P – H R ∆H = H Products – H reactants ∆H = H P – H R  ∆ H represents the Change in Enthalpy over the course of the reaction.  If ∆ H is…  …POSITIVE  The reaction is ENDOthermic.  …NEGATIVE  The reaction is EXOthermic.

Reaction Coordinate Diagrams R P ∆ H = - R P ∆ H = +

Examples Hess’s Law: ∆ H = H P – H R ∆ H = 600 J – 100 J ∆ H = J  endothermic ∆ H = H P – H R ∆ H = 200 kJ – 1000 kJ ∆ H = kJ  exothermic H R =100J H P =600J H P =200kJ H R =1000kJ

Cornell Notes (continued) A chemical reaction had reactants with 200J of energy. To get the reaction started, 600J of energy were added. Then 700J of energy are released to form the products. Trace the steps of how to draw a reaction coordinate diagram. R P Activation Energy (600J) = energy needed to make the reaction happen spontaneously ∆H = H P – H R ∆H = 100J – 200J ∆H = -100J  exothermic ∆H∆H

Example: Graph to Description The reactants had J of energy. An activation energy of J was required. The products then had J of energy. Overall, the reaction was __thermic. R P endo ∆H = H P – H R ∆H = 500J – 300J ∆H = + 200J  endothermic

Example: Graph to Description The reactants had J of energy. An activation energy of J was required. The products then had J of energy. Overall, the reaction was __thermic. R P exo ∆H = H P – H R ∆H = 100J – 350J ∆H = - 250J  exothermic