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2.1 ENERGETICS ASSESSED HOMEWORK MS
1. (a)



2220 × (1)
=1 510 000 kJ (unit must be correct for value) (1)
ignore ­ve sign
do not allow kJ mol­1 for unit
penalise significant figures (other than 3 or 4) once in (a) and (b) together

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(b) (i)

the energy…

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Enthalpy change when 1 mol of compound

1
Is formed from it's elements

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All substances in their standard state

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(b) H = Hc (reactants) ­ Hc (products)

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= (7x ­ 394) + (4 x ­ 286) ­ (­ 3909)

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= + 7 kJmol­1

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(c) Heat…

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1
[15]

3. (a)

enthalpy change/ heat energy change when 1 mol of a substance

1
is completely burned in oxygen 1
at 298K and 100 kPa or standard conditions 1

(b) H = bonds broken ­ bonds formed

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= (6 × 412) + 612 +348 + (4.5 ×…

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= ­ 145 (1)

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(c) H = 3×H (CO2) + 25 × H (H2O) ­H (N.G) (1)
= 3 × ­394 + 25 × ­242 ­ (­145) (1)
= ­1642 (1)
(or H = H (N.G) ­3 × H ( ½N2) (1)
= ­1540 ­3 × 34 (1) =…

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2



(d) = 134 kJ mol­1
Mark one : 2 × (answer to (c))
Mark two : Dividing by answers to (b)
Allow 133 ­ 134
Penalise incorrect units
Mark conseq to equation in (a) for full marks, also to that in (c)
If No working is shown and answer…

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