# Energetics - A level chemistry

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#1
Hi,
I have covered most of the topic but there is one question style that I havent managed to tackle yet. I watched youtube videos to help with my understanding but it left me more confused.

For example
4. Below are some standard enthalpy changes including the standard enthalpy of combustion of nitroglycerine, C3H5N3O9
½ N2(g) + O2(g)  NO2(g) H = +34 kJ mol–1
C(s) + O2(g)  CO2(g) H = –394 kJ mol–1
H2(g) + ½O2(g)H2O(g) H = –242 kJ mol–1
C3H5N3O9(l) + O2(g) 3CO2(g) + H2O(g) + 3NO2(g) H = –1540 kJ mol–1

(a) Standard enthalpy of formation is defined using the term standard state.What does the term standard state mean?
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(2)

(b) Use the standard enthalpy changes given above to calculate the standard enthalpy of formation of nitroglycerine.
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(4)
(c) Calculate the enthalpy change for the following decomposition of nitroglycerine.
C3H5N3O9(l)  3CO2(g) + H2O(g) + N2(g) + O2(g)
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(3)
(d) Suggest one reason why the reaction in part (c) occurs rather than combustion when a bomb containing nitroglycerine explodes on impact.
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(1)
(e) An alternative reaction for the combustion of hydrogen, leading to liquid water, is given below.
H2(g) + ½O2(g)  H2O(l) H = –286 kJ mol–1
Calculate the enthalpy change for the process H2O(l)  H2O(g) and explain the sign of H in your answer.
Calculation..................... ................................ ................................ .............................
Explanation for sign of H............................ ................................ .............................
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(2)
(Total 12 marks)

What do I do with all of these values?
0
1 month ago
#2
I haven't really read the question closely but it looks like you need to do a born-haber cycle?
0
1 month ago
#3
What are your thoughts so far?
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#4
(Original post by Pyruvic Acid)
What are your thoughts so far?
I would say to rearrange the equation so everything is on the right side
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1 month ago
#5
(Original post by Sclaremonths)
I would say to rearrange the equation so everything is on the right side
I believe this thread tackles the same question that you're stuck on: https://www.thestudentroom.co.uk/sho....php?t=1533312

Feel free to ask if you still need help
0
#6
Thank you!so in general i would add the values up for questions like this
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