2. 1 Energetics Test

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"Energy Rush"
Y12 Unit 2 Test 1
2.1 Energetics
Sa srecom!
Answer all questions
Total 50 marks
Name:.................................................
Section A........../35
Section B........../15
TOTAL .................../50
= .......................%
Grade __________

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SECTION A
1. The table below contains some mean bond enthalpy data.
Bond HH CC C=C NN NH
Mean bond enthalpy / kJ mol­1 436 348 612 944 388
(a) Explain the term mean bond enthalpy.
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(2)
(b) (i) Write an equation for the formation of one mole of ammonia, NH3, from its
elements.
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(ii) Use data from the table above to calculate a value for the enthalpy of formation of
ammonia.
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The table below contains some mean bond enthalpy data.
Bond H­O O­O O=O
Mean bond enthalpy/kJ mol­1 463 146 496
The bonding in hydrogen peroxide, H2O2, can be represented by H­O­O­H. Use these
data to calculate the enthalpy change for the following reaction.
H2O2(g) H2O(g) + O2(g)
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(3)
(b) The standard enthalpy of formation, Hf for methane, is ­74.9 kJ mol­1. Write an
equation, including state symbols, for the reaction to which this enthalpy change applies.
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Parts (b) and (c) give enthalpy data for the formation of CH4(g), H(g) and
C(g).
Use these data and Hess's Law to calculate the value of the enthalpy change for
the following reaction.
CH4(g) C(g) + 4H(g)
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(iii) Use your answer from part (c)(ii) to calculate a value for the mean bond enthalpy
of a C­H bond in methane.
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(5)
(Total 10 marks)
3. (a) Define the term standard enthalpy of combustion.
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Use the standard enthalpies of formation given below to calculate the
standard enthalpy of combustion of ethane.
Formula and state of compound C2 CO H2
H6( 2(g) O(l
g) )
Standard enthalpy of formation (at 298 K) /kJ ­85 ­39 ­28
mol­1 4 6
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(4)
(Total 6 marks)
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Burning 2.5 g of methylbenzene caused the temperature of 250 g of water to rise by
60°C. Use this information to calculate a value for the enthalpy of combustion of
methylbenzene, C7H8
(The specific heat capacity of water is 4.18 J K­1 g­1. Ignore the heat capacity of the
container.)
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(3)
(c) Calculate a value for the standard enthalpy of formation for liquid ethanethiol,C2H5SH.…read more

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SECTION B
5. (a) Define the term standard enthalpy of formation.
(3)
(b) State Hess's Law and use it, together with the data given in the table below, to calculate
the standard enthalpy change for the following reaction.
MgO(s) + 2HCl(g) MgCl2(s) + H2O(l)
MgO HCl(g) MgCl2 H2O
Hf /kJ mol­1 ­602 ­92 ­642 ­286
(4)
(c) In an experiment, an excess of solid magnesium oxide was added to 50 cm3 of
3.0 mol dm­3 hydrochloric acid.…read more

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