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9 (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 - Question 9 - 2022 - Paper 1

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9 (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:9 (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 - Question 9 - 2022 - Paper 1

Step 1

i) Which row is correct about the energy changes for these processes?

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Answer

The correct answer is B: breaking a bond involves energy being absorbed, while making a bond involves energy being released. This reflects the fundamental principles of bond formation and breaking.

Step 2

ii) Hydrogen reacts with fluorine.

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Answer

To calculate the overall energy change for the reaction, we follow these steps:

  1. Calculate the total bond energy of the reactants:

    • Bonds in H₂: 1 H–H bond = 436 kJ/mol
    • Bonds in F₂: 1 F–F bond = 562 kJ/mol
    • Total energy for reactants = 436 + 562 = 998 kJ/mol.

  2. Calculate the total bond energy of the products:

    • Bonds in 2HF: 2 H–F bonds = 2 × 158 = 316 kJ/mol.

  3. Calculate the overall energy change:

    • Overall energy change = Energy in reactants - Energy in products = 998 - 316 = 682 kJ/mol.

This shows that the reaction is exothermic, as energy is released when forming the new bonds in the products.

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