WAEC Chemistry questions: Energy changes

16 questions with answers and explanations. Tap an option to check yourself.

1. Question 1· Energy changes· WAEC

   Which combination makes a reaction spontaneous (ΔG negative) at every temperature?

   • Apositive ΔH and negative ΔS
   • Bnegative ΔH and positive ΔS
   • Cpositive ΔH and positive ΔS
   • Dnegative ΔH and negative ΔS

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2. Question 2· Energy changes· WAEC

   Dissolving ammonium chloride in water makes the beaker feel cold. The process is

   • Aa neutralisation
   • Bexothermic
   • Ca redox reaction
   • Dendothermic

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3. Question 3· Energy changes· WAEC

   The heat of combustion of a substance is the heat

   • Aevolved when one mole burns completely in oxygen
   • Babsorbed when one mole melts
   • Cevolved on dissolving
   • Dneeded to boil one mole

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4. Question 4· Energy changes· WAEC

   Dissolving ammonium nitrate in water makes the solution cold because the process is

   • Aa combustion
   • Bexothermic
   • Cendothermic
   • Dneutralisation

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5. Question 5· Energy changes· WAEC

   A reaction in which heat is absorbed from the surroundings is

   • Areversible
   • Bexothermic
   • Ccatalytic
   • Dendothermic

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6. Question 6· Energy changes· WAEC

   50 cm³ of 1.0 mol/dm³ HCl is mixed with 50 cm³ of 1.0 mol/dm³ NaOH and 2.85 kJ of heat is released. Find the heat of neutralisation.

   • A−114 kJ/mol
   • B−2.85 kJ/mol
   • C−28.5 kJ/mol
   • D−57 kJ/mol

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7. Question 7· Energy changes· WAEC

   When ammonium chloride dissolves in water, the solution becomes cold. The process is

   • Aexothermic
   • Bneutralisation
   • Cendothermic
   • Dcombustion

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8. Question 8· Energy changes· WAEC

   In an exothermic reaction, the energy of the products is

   • Aless than that of the reactants
   • Bgreater than that of the reactants
   • Cequal to that of the reactants
   • Dzero

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9. Question 9· Energy changes· WAEC

   Burning butane in a gas cooker is described as exothermic because

   • Ait needs a spark to start
   • Bheat is absorbed from the surroundings
   • Cheat is given out to the surroundings
   • Dthe products are gases

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10. Question 10· Energy changes· WAEC

    Heat released when 2 mol of a substance burns is 1,600 kJ. Find the heat of combustion per mole.

    • A−1,600 kJ/mol
    • B−800 kJ/mol
    • C−3,200 kJ/mol
    • D+800 kJ/mol

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11. Question 11· Energy changes· WAEC

    An energy profile diagram where the products are higher in energy than the reactants represents

    • Aa neutral reaction
    • Ban exothermic reaction
    • Can endothermic reaction
    • Da catalysed reaction only

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12. Question 12· Energy changes· WAEC

    A reaction that gives out heat to the surroundings is

    • Aendothermic
    • Bexothermic
    • Creversible
    • Dcatalytic

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13. Question 13· Energy changes· WAEC

    Activation energy is the

    • Aenergy released by a reaction
    • Bminimum energy needed for a reaction to occur
    • Cheat of solution
    • Dbond length

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14. Question 14· Energy changes· WAEC

    Which of these processes is endothermic?

    • Aburning of wood
    • Bmelting of ice
    • Crusting of iron
    • Drespiration

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15. Question 15· Energy changes· WAEC

    The heat change when one mole of water is formed from the neutralisation of an acid by a base is the heat of

    • Acombustion
    • Bneutralisation
    • Cformation
    • Dsolution

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16. Question 16· Energy changes· WAEC

    For C + O₂ → CO₂, ΔH = −394 kJ/mol. How much heat is released when 6 g of carbon burns completely? [C = 12]

    • A197 kJ
    • B394 kJ
    • C788 kJ
    • D65.7 kJ

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    Explanation and discussion