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
3. 3.

   Burning ethanol releases 1366.8 kJ per mole. How much heat is released when 0.5 mol of ethanol burns, Esme?

   683.4 kJ
4. 4.

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

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

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

   • Agree: heat leaves the hand, so it's exothermic
   • Disagree: the pack takes in that heat
   • Agree: cold things give off cold
6. 6.

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

   • Disagree: the warmer gives out heat
   • Agree: the hand takes heat in, so it's endothermic
   • Agree: iron soaks up the warmth
7. 7.

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

   • Disagree: it still has a hill
   • Agree: heat comes out, so nothing goes in
   • Agree: exothermic means no hill
8. 8.

   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
   • Ethanol
   • Methane
9. 9.

   Making liquid water releases 286 kJ per mole; making water vapor releases 242 kJ. Why is there a difference, Tala?

   • Condensing also releases heat
   • Vapor forms more slowly
   • Vapor has no bonds in it
10. 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