Enthalpy Changes in ChemistryEnthalpy Changes in Chemistry

HeatHeat

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

1.Exothermic: when heat is given out2.Endothermic: 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

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)

exo

Sugar and sulfuric acid

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

N/A (demo)

N/A (demo)

N/A (demo)

exo

Dissolving ammonium nitrate

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

N/A (demo)

N/A (demo)

N/A (demo)

endo

Barium hydroxide and ammonium nitrate

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

N/A (demo)

N/A (demo)

N/A (demo)

endo

Exothermic ReactionsExothermic Reactions

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?

3 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