Lesson 1 - Enthalpy Changes in Chemistry

Lesson 1 - Enthalpy Changes in Chemistry

StarterStarter

• When a chemical reaction takes place heat may be given out or taken in.

1.Can you remember the word we use when heat is given out?

2.Can you remember the word we use when heat is taken in?

Energy level diagramsEnergy level diagrams

Heat taken inHeat taken in Heat given outHeat given out

Change in energyChange in energy

ObjectivesObjectives

MustRecall and use the terms ENDOTHERMIC and EXOTHERMICShouldDescribe examples of ENDOTHERMIC and EXOTHERMIC reactions.CouldExplain ENDOTHERMIC and EXOTHERMIC reactions using energy level diagrams.

Reactants Description of reaction Initial temp. / °C

Final temp. /°C

Change in temp. ΔT / °C

Exo or endo?

Sodium and chlorine gas

https://www.youtube.com/watch?v=Mx5JJWI2aaw

N/A (demo)

N/A (demo)

N/A (demo)

Sugar and sulfuric acid

https://www.youtube.com/watch?v=nqDHwd9rG0s

N/A (demo)

N/A (demo)

N/A (demo)

Dissolving ammonium nitrate

https://www.youtube.com/watch?v=G3S4YvhhAic

N/A (demo)

N/A (demo)

N/A (demo)

Barium hydroxide and ammonium nitrate

https://www.youtube.com/watch?v=GQkJI-Nq3Os

N/A (demo)

N/A (demo)

N/A (demo)

DefinitionsDefinitions

Exothermic ReactionsExothermic Reactions

DefinitionsDefinitions

Endothermic ReactionsEndothermic Reactions

Which of the following statements is correct?

Which of the following statements is correct?

1. The products of a chemical reaction have more energy than the reactants so an exothermic reaction must have taken place.

2. The products of a chemical reaction have less energy than the reactants so an endothermic reaction must have taken place.

3. The products of a chemical reaction have less energy than the reactants so an exothermic reaction must have taken place.

1. The products of a chemical reaction have more energy than the reactants so an exothermic reaction must have taken place.

2. The products of a chemical reaction have less energy than the reactants so an endothermic reaction must have taken place.

3. The products of a chemical reaction have less energy than the reactants so an exothermic reaction must have taken place.

Which of the following statements is correct?

Which of the following statements is correct?

The products of a chemical reaction have less energy than the reactants so an exothermic reaction must have taken place.

Q - How can we illustrate this?

Energy level diagrams – copy into your notes

Energy level diagrams – copy into your notes

Endothermic Exothermic

Heat taken inHeat taken in Heat given outHeat given out

Energy level of products is higher than reactants so heat taken in.Energy level of products is higher than reactants so heat taken in.

Energy level of products is lower than reactants so heat given out.Energy level of products is lower than reactants so heat given out.

QuestionQuestion

AnswerAnswer

Wrap up – Can you recall?Wrap up – Can you recall?

• Draw an energy profile for an exothermic reaction marking clearly the activation energy.