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b)
State the type of system in which the total amount of matter present is always constant.
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c)
Using the image below, construct an equation that can be used to determine ΔHr from ΔH1 and ΔH2 .
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d)
Complete the following Hess’s Law cycle for the decomposition of copper carbonate.
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a)
Define standard enthalpy of formation, ΔHf .
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b)
Write an equation to show the enthalpy of formation of 1 mole of the following compounds. Include state symbols in your equations.
Methanol, CH3 OH ………………………………..
Carbon dioxide, CO2 ………………………………..
Ethane, C2 H6 ………………………………..
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c)
Using the equations given, construct a Hess’s Law cycle for the following reaction. Include the values for ΔHf in your cycle.
BaCl2 (s) + Zn (s) → Ba (s) + ZnCl2 (s)
Ba (s) + Cl2 (g) → BaCl2 (s) ΔHf = -858.6 kJ mol-1
Zn (s) + Cl2 (g) → ZnCl2 (s) ΔHf = -415.1 kJ mol-1
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d)
Calculate the enthalpy of reaction, ΔHr , for the reaction given in part (c).
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a)
Aluminium oxide reacts with magnesium to form magnesium oxide and aluminium in a displacement reaction via the following reaction.
Construct a Hess’s Law cycle for this reaction
Al2 O3 (s) + 3Mg (s) → 3MgO (s) + 2Al (s)
Enthalpy of formation Enthalpy of formation (kJ mol-1 )
ΔHf (Al2 O3 )
-1675.7
ΔHf (MgO)
-601.7
ΔHf (Mg)
ΔHf (Al)
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b)
Outline why no values are listed for Al (s) and Mg (s) in the table given in part (a).
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c)
Calculate the enthalpy change of reaction, ΔHr , for the reaction in part (a).
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a)
Determine the enthalpy change of reaction, ΔHr , for the following equations if they are reversed.
2Na + Cl2 → 2NaCl ΔHr = -790 kJ ……………………….
C2 H4 + H2 → C2 H6 ΔHr = -65.6 kJ ………………………
2H 2 O → 2H 2 + O2 ΔHr = +571 kJ ……………………….
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b)
Using the information given in part (a), determine the enthalpy change for the following reaction.
2C2 H4 + 2H2 → 2C2 H6
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c)
Using the information in the table, deduce which equation should be reversed to determine the enthalpy change for the following reaction.
SiO2 + 3C → SiC + 2CO
Equation number Equation Enthalpy change (kJ)
1
Si + O2 → SiO2
-911
2
2C + O2 → 2CO
-211
3
Si + C → SiC
-65.3
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d)
Use the information in part (c) to produce an overall cancelled down equation which can be used to determine the overall enthalpy change for the following reaction.
SiO2 + 3C → SiC + 2CO
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e)
Deduce the overall enthalpy change, in kJ, using the information in part (c) for the reaction SiO2 + 3C → SiC + 2CO
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a)
State the equation required to calculate the enthalpy change of reaction, ΔHr , given enthalpy of formation, ΔH f
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b)
Using section 12 in the data booklet and the data in the table calculate the enthalpy change of reaction, ΔHr , for the following reaction.
SO2 (g) + 2H2 S (g) → 3S (s) + 2H2 O (l)
SO2 (g) H2 S (g)
ΔH f (kJ mol-1 ) -297
-20.2
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c)
Show how the equations can be used to produce an alternative route for this reaction .
C2 H4 + H2 → C2 H6
ΔH (kJ mol-1 )
C2 H4 + 3O2 → 2CO2 + 2H2 O
-1411
C2 H6 + 3½O2 → 2CO2 (g) + 3H2 O
-1560
H2 + ½O2 → H2 O
-285.8
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