Module 3 Lesson 1 - Enthalpy Changes in Chemistry

Starter 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?

AfL - Energy level diagrams Heat taken in Heat given out

Change in energy

Objectives Must Recall and use the terms ENDOTHERMIC and EXOTHERMIC Should Describe examples of ENDOTHERMIC and EXOTHERMIC reactions. Could Explain ENDOTHERMIC and EXOTHERMIC reactions using energy level diagrams.

ReactantsDescription of reactionInitial temp. / °C Final temp. /°C Change in temp. ΔT / °C Exo or endo? Sodium and chlorine gas N/A (demo) Sugar and sulphuric acid N/A (demo) Dissolving ammonium nitrate N/A (demo) Barium hydroxide and ammonium nitrate N/A (demo)

Exothermic Demos Chlorine gas reacting with sodium metal (video) Concentrated sulphuric acid and sugar (demo)

Definitions

Exothermic Reactions

Endothermic Demos Dissolving ammonium nitrate Reaction between ammonium nitrate and barium hydroxide.

Definitions

Endothermic Reactions

AfL - 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? 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 EndothermicExothermic Heat taken in Heat given out Energy level of products is higher than reactants so heat taken in. Energy level of products is lower than reactants so heat given out.

Question

Answer

Plenary – Can you recall? Draw an energy profile for an exothermic reaction marking clearly the activation energy.

Homework Question booklet.