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This question is about ammonia, NH₃ Complete the dot and cross diagram for the ammonia molecule shown in Figure 6 - AQA - GCSE Chemistry - Question 5 - 2019 - Paper 1
Question 5
This question is about ammonia, NH₃ Complete the dot and cross diagram for the ammonia molecule shown in Figure 6. Show only the electrons in the outer shell of eac... show full transcript
Worked Solution & Example Answer:This question is about ammonia, NH₃ Complete the dot and cross diagram for the ammonia molecule shown in Figure 6 - AQA - GCSE Chemistry - Question 5 - 2019 - Paper 1
Step 1
Complete the dot and cross diagram for the ammonia molecule shown in Figure 6.
Answer
In the dot and cross diagram for the ammonia molecule (NH₃), nitrogen (N) has five outer shell electrons, while each hydrogen (H) has one outer shell electron. The diagram should show the nitrogen atom in the center with three hydrogen atoms around it, sharing electrons. The nitrogen atom would have a distinct pair of electrons to represent the lone pair, while each hydrogen would share their single electron with nitrogen to form three N-H bonds.
Step 2
Step 3
Explain why ammonia has a low boiling point.
Answer
Ammonia has a low boiling point due to weak intermolecular forces known as Van der Waals forces. Although ammonia can form hydrogen bonds, these bonds are relatively weak compared to covalent bonds, meaning that not much energy is required to overcome them. Therefore, it exists as a gas at room temperature and has a low boiling point.
Step 4
Step 5
Calculate the overall energy change for the reaction.
Answer
To calculate the overall energy change:
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Calculate the total energy required to break the bonds in the reactants:
- Bonds broken: (4 N-H bonds) + (3 O=O bonds)
- Energy required = (4 × 391 kJ/mol) + (3 × 498 kJ/mol) = 6186 kJ.
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Calculate the total energy released when new bonds are formed in the products:
- Bonds formed: (2 N≡N bonds) + (6 O-H bonds)
- Energy released = (2 × 945 kJ/mol) + (6 × 464 kJ/mol) = 7458 kJ.
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Overall energy change = Energy released - Energy required = 7458 kJ - 6186 kJ = 1272 kJ (which is exothermic, hence written as -1272 kJ).
Step 6
Explain why the reaction between ammonia and oxygen is exothermic.
Answer
The reaction between ammonia and oxygen is exothermic because it releases energy to the surroundings. The energy released when new bonds are formed in the products exceeds the energy required to break the bonds in the reactants. As calculated, the overall energy change was -1272 kJ, indicating that the reaction releases heat.
Step 7
Complete Figure 8 by labelling the: activation energy and overall energy change.
Answer
In Figure 8, the activation energy can be labelled at the peak of the reaction profile, showing the energy barrier that must be overcome for the reaction to occur. The overall energy change label should be positioned to indicate the energy difference between the reactants and products, which would be marked as -1272 kJ, illustrating that energy is released during the reaction.