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Enthalpy of formation
Hi,
Can someone please help me? Its part (iii) I need help on I just thought I'd provide the follow upquesitons to it.
The structure of hydrazine can be represented as shown below.
(a) (i) Write an equation for the formation of hydrazine from its elements.
............................................................................................................................
(ii) Steam and nitrogen gas are the combustion products of gaseous hydrazine.
Write an equation for this reaction.
............................................................................................................................
(iii) Use the data given below to calculate the standard enthalpy of formation of gaseous hydrazine.
(enthalpy of combustion) N2H4(g) = –568 kJ mol–1
(enthalpy of formation) H2O(g) = –242 kJ mol–1
The answer is 84 kJ mol–1 but I really don't know how to get the answer. How do I combine both enthalpy of combustion and formation? In the mark scheme they'ev provided this diagram:
http://www.a-levelchemistry.co.uk/AQA%20Chemistry/AQA%20AS%20Chemistry/Unit%202/2.1%20Energetics/2.1%20Energetics%20database.rtf
(question 17)
I'd have copied and pasted the answer but it comes out all funny, but anyway the diagram is so confusing. I'd really appreciate any explanation of it and how to get the answer.
Thankyou
Can someone please help me? Its part (iii) I need help on I just thought I'd provide the follow upquesitons to it.
The structure of hydrazine can be represented as shown below.
(a) (i) Write an equation for the formation of hydrazine from its elements.
............................................................................................................................
(ii) Steam and nitrogen gas are the combustion products of gaseous hydrazine.
Write an equation for this reaction.
............................................................................................................................
(iii) Use the data given below to calculate the standard enthalpy of formation of gaseous hydrazine.
(enthalpy of combustion) N2H4(g) = –568 kJ mol–1
(enthalpy of formation) H2O(g) = –242 kJ mol–1
The answer is 84 kJ mol–1 but I really don't know how to get the answer. How do I combine both enthalpy of combustion and formation? In the mark scheme they'ev provided this diagram:
http://www.a-levelchemistry.co.uk/AQA%20Chemistry/AQA%20AS%20Chemistry/Unit%202/2.1%20Energetics/2.1%20Energetics%20database.rtf
(question 17)
I'd have copied and pasted the answer but it comes out all funny, but anyway the diagram is so confusing. I'd really appreciate any explanation of it and how to get the answer.
Thankyou
Original post by interact
Hi,
Can someone please help me? Its part (iii) I need help on I just thought I'd provide the follow upquesitons to it.
The structure of hydrazine can be represented as shown below.
(a) (i) Write an equation for the formation of hydrazine from its elements.
............................................................................................................................
(ii) Steam and nitrogen gas are the combustion products of gaseous hydrazine.
Write an equation for this reaction.
............................................................................................................................
(iii) Use the data given below to calculate the standard enthalpy of formation of gaseous hydrazine.
(enthalpy of combustion) N2H4(g) = –568 kJ mol–1
(enthalpy of formation) H2O(g) = –242 kJ mol–1
The answer is 84 kJ mol–1 but I really don't know how to get the answer. How do I combine both enthalpy of combustion and formation? In the mark scheme they'ev provided this diagram:
http://www.a-levelchemistry.co.uk/AQA%20Chemistry/AQA%20AS%20Chemistry/Unit%202/2.1%20Energetics/2.1%20Energetics%20database.rtf
(question 17)
I'd have copied and pasted the answer but it comes out all funny, but anyway the diagram is so confusing. I'd really appreciate any explanation of it and how to get the answer.
Thankyou
Can someone please help me? Its part (iii) I need help on I just thought I'd provide the follow upquesitons to it.
The structure of hydrazine can be represented as shown below.
(a) (i) Write an equation for the formation of hydrazine from its elements.
............................................................................................................................
(ii) Steam and nitrogen gas are the combustion products of gaseous hydrazine.
Write an equation for this reaction.
............................................................................................................................
(iii) Use the data given below to calculate the standard enthalpy of formation of gaseous hydrazine.
(enthalpy of combustion) N2H4(g) = –568 kJ mol–1
(enthalpy of formation) H2O(g) = –242 kJ mol–1
The answer is 84 kJ mol–1 but I really don't know how to get the answer. How do I combine both enthalpy of combustion and formation? In the mark scheme they'ev provided this diagram:
http://www.a-levelchemistry.co.uk/AQA%20Chemistry/AQA%20AS%20Chemistry/Unit%202/2.1%20Energetics/2.1%20Energetics%20database.rtf
(question 17)
I'd have copied and pasted the answer but it comes out all funny, but anyway the diagram is so confusing. I'd really appreciate any explanation of it and how to get the answer.
Thankyou
This is the combustion equation:
N2H4 + O2 --> N2 + 2H2O
Imagine that the reactants are all turned to elements (in their standard states) and from there turned to the products...
How would the energy changes be then?
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