What are the standard units of energy? What units of energy are mostly used in Chemistry?

1. QQ What are the standard units of energy? What units of energy are mostly used in Chemistry? What is another term for heat energy of a reaction? How can changes in heat energy of reactions be detected? Give a biochemical reaction which releases heat energy.

2. Natural Energetics

3. Topic 5: EnergeticsLesson 1: Enthalpy Objectives (Ref SGp28) 5.1.1 Define the terms exothermic reaction, endothermic reaction and standardenthalpy change of reaction (∆Hө) 5.1.2 State that combustion and neutralization are exothermic processes. 5.1.3 Apply the relationship between temperature change, enthalpy change and the classification of a reaction as endothermic or exothermic. 5.1.4 Deduce, from an enthalpy level diagram, the relative stabilities of reactants and products, and the sign of the enthalpy change for the reaction.

4. Enthalpy Enthalpy is the heat energy of a reaction. Only changes in enthalpy can be measured. Standard enthalpy change (∆Hө) “is the heat energytransferred under standard conditions” pressure of 101.3 kPa (1 atm) temperature 298 K (25 ◦C)

5. Exothermic enthalpy changes Reactants → Products Hreactants > Hproducts, ∆H = Hp – Hr so, ∆H is negative, heat energy is given out so the temperature of the container increases. This can be shown in an Energy Level Diagram.

6. Energy level diagrams for specific exothermic reactions Spontaneous reaction – the reactants are unstable Reaction requiring initial heating first – the reactants are stable

7. Neutralisation and Combustion are both types of exothermic reactions E.g. HCl + NaOH → NaCl + H2O, ∆H -ve 1. Write 2 more and draw an Energy Level Diagram for each. E.g. CH4 + 2O2→ CO2 + 2H20, ∆H -ve 2. Write 2 more with an Energy Level Diagram for each.

8. Endothermic enthalpy changes Reactants → Products Hreactants < Hproducts, ∆H = Hp – Hr so, ∆H is positive , heat energy is taken in so the temperature of the container decreases. This can be shown in an Energy Level Diagram.

9. Energy level diagrams for specific endothermic reactions G&D p137 for a further example

10. Further work In class At home G+D P137 Q1-3 P137 Ex 5.1 Q4+5 due Monday 20 January 2014.

11. Plenary Can we? Next time- • Define the terms exothermic reaction, endothermic reaction and standard enthalpy change of reaction (∆Hө) • State that combustion and neutralization are exothermic processes. • The classification of a reaction as endothermic or exothermic. • Deduce, from an enthalpy level diagram, the relative stabilities of reactants and products, and the sign of the enthalpy change for the reaction. • Calculations on Enthalpy.