The reaction between nitrogen, N₂, and hydrogen, H₂, to form ammonia, NH₃, is an exothermic reaction which is shown in this equation. H N≡N + 3H₂ ⇌ 2NH₃ The table shows some bond energies. | Bond | Bond energy (kJ/mol) | | ----- | --------------------- | | N≡N | 945 | | H–H | 435 | | N–H | 390 | (a) (i) Calculate the total energy transferred to break all the bonds in the reactants. Energy transferred to break all the bonds = .................................... kJ/mol [1] (ii) Calculate the total energy transferred when all the bonds in the products are made. Energy transferred when all the bonds are made = .................................. kJ/mol [1] (iii) Use your answers to parts (i) and (ii) to calculate the energy change for the reaction. Energy change = .............................................................. kJ/mol [1]

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The reaction between nitrogen, N₂, and hydrogen, H₂, to form ammonia, NH₃, is an exothermic reaction which is shown in this equation - OCR Gateway - GCSE Chemistry: Combined Science - Question 16 - 2023 - Paper 9

Question 16

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The reaction between nitrogen, N₂, and hydrogen, H₂, to form ammonia, NH₃, is an exothermic reaction which is shown in this equation. H N≡N + 3H₂ ⇌ 2NH₃ The table ... show full transcript

Worked Solution & Example Answer:The reaction between nitrogen, N₂, and hydrogen, H₂, to form ammonia, NH₃, is an exothermic reaction which is shown in this equation - OCR Gateway - GCSE Chemistry: Combined Science - Question 16 - 2023 - Paper 9

Step 1

(i) Calculate the total energy transferred to break all the bonds in the reactants.

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Answer

To calculate the energy required to break all the bonds in the reactants, we need to consider the bonds present:

The nitrogen-nitrogen triple bond (N≡N), which has a bond energy of 945 kJ/mol.
There are three hydrogen-hydrogen bonds (H–H), each with a bond energy of 435 kJ/mol.

The total energy for the reactants will be:

$ext{Total Energy} = ext{Bond Energy}(N≡N) + 3 imes ext{Bond Energy}(H–H)$

Substituting the values:

$ext{Total Energy} = 945 + 3 imes 435 = 945 + 1305 = 2250 ext{ kJ/mol}$

Thus, the energy transferred to break all the bonds in the reactants is 2250 kJ/mol.

Step 2

(ii) Calculate the total energy transferred when all the bonds in the products are made.

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Answer

For the products, we have 2 ammonia (NH₃) molecules. Each NH₃ molecule has three N–H bonds, so the total N–H bonds in the products is:

$ext{Total N–H Bonds} = 2 imes 3 = 6 ext{ N–H bonds}$

The bond energy for N–H is 390 kJ/mol. Therefore, the total energy released when the bonds are formed is:

$ext{Total Energy} = 6 imes ext{Bond Energy}(N–H)$

Substituting the value:

$ext{Total Energy} = 6 imes 390 = 2340 ext{ kJ/mol}$

Thus, energy transferred when all the bonds are made is 2340 kJ/mol.

Step 3

(iii) Use your answers to parts (i) and (ii) to calculate the energy change for the reaction.

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Answer

The energy change for the reaction can be calculated using the formula:

$ext{Energy Change} = ext{Energy Required to Break Bonds} - ext{Energy Released in Forming Bonds}$

Substituting the values from parts (i) and (ii):

$ext{Energy Change} = 2250 ext{ kJ/mol} - 2340 ext{ kJ/mol} = -90 ext{ kJ/mol}$

Therefore, the energy change for the reaction is -90 kJ/mol.

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