Starter

Balance the following complete combustion equations1)C2H6 + O2

2)C10H22 + O2

Extension3) CH3SH + O2

Starter

1) What are standard conditions?

2) Classify as endothermic or exothermic.a) Combustion of methaneb) Respirationc) Photosynthesisd) NaOH + HCl

Determination of Enthalpy Changes

L.O.:Define and use the terms: standard conditions; enthalpy change of reaction; enthalpy change of formation; and enthalpy change of combustion.

Standard enthalpy change of formation , ∆Hѳf , of a

compound is the enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard state under standard conditions.

•Example(s):C(s,graphite) + O2(g) ———> CO2(g)H2(g) + ½O2(g) ———> H2O(l)

2C(s,graphite) + ½O2(g) + 3H2(g) ——>C2H5OH(l)

Task:Write equations for standard enthalpy change

of formation for

1)C3H8

2)MgO3)Ethanol4)Al2O3

Standard enthalpy change of combustion, ∆Hѳc , is the

enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard state.

Example(s):C(s, graphite) + O2(g) ———> CO2(g)

H2(g) + ½O2(g) ———> H2O(l)

C2H5OH(l) + 3O2(g) ———> 2CO2(g) + 3H2O(l)

Task:Write equations for the change that occurs

during the enthalpy change of formation of:1)CH4

2)MgO3)Ethanol4)Al2O3

L.O.:Calculate enthalpy changes directly from

appropriate experimental results, including the use of the relationship: energy change = mcΔT.

An excess of magnesium is added to to 100cm3 of 2.00 mol dm-3

CuSO4(aq). The temperature increases from 20.0 to 65.0 oC.

Find the enthalpy change for this reaction(c= 4.18 Jg-1k-1)

1)Energy change (Q)Q = mc T

2) Find out the amount, in mol, that reacted3) DH=Q/n4) Work out sign.

• Allan’s 3.3

EXTENSION