# Enthalpy Question - URGENT

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Hi,

I was attempting this test paper. I got this question wrong but I don't understand the maths of the mark scheme could someone help explain it to me?

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Markscheme:

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Also, if the data given to you is the mean bond enthalpy but it asks you to work out the enthalpy of formation do you use products- reactants or bonds broken - bonds formed

I was attempting this test paper. I got this question wrong but I don't understand the maths of the mark scheme could someone help explain it to me?

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Markscheme:

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Also, if the data given to you is the mean bond enthalpy but it asks you to work out the enthalpy of formation do you use products- reactants or bonds broken - bonds formed

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#2

(Original post by

Hi,

I was attempting this test paper. I got this question wrong but I don't understand the maths of the mark scheme could someone help explain it to me?

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Markscheme:

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Also, if the data given to you is the mean bond enthalpy but it asks you to work out the enthalpy of formation do you use products- reactants or bonds broken - bonds formed

**Sclaremonths**)Hi,

I was attempting this test paper. I got this question wrong but I don't understand the maths of the mark scheme could someone help explain it to me?

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Markscheme:

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Also, if the data given to you is the mean bond enthalpy but it asks you to work out the enthalpy of formation do you use products- reactants or bonds broken - bonds formed

0

reply

Report

#3

**Sclaremonths**)

Hi,

I was attempting this test paper. I got this question wrong but I don't understand the maths of the mark scheme could someone help explain it to me?

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Markscheme:

3. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

.............................................................................................................

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

(4)

(b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

(3)

(Total 7 marks)

Also, if the data given to you is the mean bond enthalpy but it asks you to work out the enthalpy of formation do you use products- reactants or bonds broken - bonds formed

1

reply

Report

#4

for enthalpy change you do products - reactants

and for energy change you do bonds broken- bonds made

and for energy change you do bonds broken- bonds made

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