Reactions that release or absorb energy

Answer Key - Grade 10 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   Forming liquid water from hydrogen releases 286 kJ per mole of water. How much heat is released when 3 mol of water forms, Ari?

   858 kJ
2. 2.

   Burning methane releases 890.8 kJ per mole. How much heat is released when 2 mol of methane burns, Bo?

   1781.6 kJ
4. 3.

   Using the diagram, what is ΔH for this reaction, Jun?

   • −40 kJ
   • +80 kJ
   • +40 kJ
5. 4.

   Using the diagram, what is the activation energy of the reverse reaction, Kira?

   Use the picture in question 3.

   • 80 kJ
   • 40 kJ
   • 130 kJ
6. 5.

   Using the diagram, is this reaction endothermic, Luz?

   Use the picture in question 3.

   • No: products are 40 kJ lower
   • No: the hill is too tall
   • Yes: products are 40 kJ higher
7. 6.

   Milo says a cold pack is exothermic because heat leaves the hand. Agree or disagree?

   • Disagree: the pack takes in that heat
   • Agree: heat leaves the hand, so it's exothermic
   • Agree: cold things give off cold
8. 7.

   Noah says a hand warmer is endothermic because the hand absorbs heat. Agree or disagree?

   • Agree: iron soaks up the warmth
   • Disagree: the warmer gives out heat
   • Agree: the hand takes heat in, so it's endothermic
9. 8.

   Pia says an exothermic reaction needs no energy to get started. Agree or disagree?

   • Agree: exothermic means no hill
   • Agree: heat comes out, so nothing goes in
   • Disagree: it still has a hill
10. 9.

    Per mole, methane burning has ΔH = −890.8 kJ and ethanol −1366.8 kJ. Which releases more heat per mole, Ren?

    • They release the same
    • Methane
    • Ethanol
11. 10.

    H₂ + ½ O₂ → H₂O(l) has ΔH = −286 kJ. What is ΔH for 2 H₂ + O₂ → 2 H₂O(l), Zee?

    • +572 kJ
    • −286 kJ
    • −572 kJ