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6 (a) In some chemical reactions, bonds are broken in the reactant molecules and new bonds are formed to make the product molecules - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2022 - Paper 1
Question 6
6 (a) In some chemical reactions, bonds are broken in the reactant molecules and new bonds are formed to make the product molecules. (i) Which row is correct about ... show full transcript
Worked Solution & Example Answer:6 (a) In some chemical reactions, bonds are broken in the reactant molecules and new bonds are formed to make the product molecules - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2022 - Paper 1
Step 1
Which row is correct about the energy changes for these processes?
Answer
In chemical reactions, when bonds are broken, it generally requires energy, hence this process absorbs energy. Conversely, forming new bonds often releases energy. Therefore:
- Correct Row: The correct option would be C: breaking a bond is energy is absorbed and making a bond is energy is released.
Step 2
Calculate the overall energy change for the reaction between hydrogen and fluorine.
Answer
For the reaction H₂ + F₂ → 2HF, we need to calculate the total bond energy changes:
-
Bonds broken:
- H–H bond: 436 kJ/mol
- F–F bond: 562 kJ/mol
- Total energy input = 436 + 562 = 998 kJ/mol
-
Bonds formed:
- There are 2 H–F bonds formed: 2 × 158 kJ/mol = 316 kJ/mol
-
Overall energy change:
- Energy change = Total energy input - Total energy released
- Energy change = 998 - 316 = 682 kJ/mol (this value indicates that the reaction is endothermic, as energy is absorbed in breaking the bonds).