Reactions that release or absorb energy

Answer Key - Grade 10 Science Worksheet - Building Confidence

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

1. 1.

   An energy diagram shows the reactants at 120 kJ and the products at 40 kJ. What is ΔH, Ari?

   -80 kJ
2. 2.

   An energy diagram shows the reactants at 50 kJ and the products at 90 kJ. What is ΔH, Bo?

   40 kJ

3. Read this first

   Energy diagram: a hill from reactants to products (example values)

   point	energy (kJ)
   reactants	120
   top of the hill	180
   products	40

4. 3.

   Using the diagram, what is the climb from the reactants to the top called, Kira?

   • Enthalpy change
   • Bond length
   • Activation energy
5. 4.

   Using the diagram, what sign does ΔH have, Luz?

   • Negative
   • Zero
   • Positive
6. 5.

   An opened hand warmer gets warm as iron reacts with oxygen. Is that exothermic or endothermic, Milo?

   • Endothermic: it is a solid
   • Exothermic: it releases heat
   • Endothermic: it releases heat
7. 6.

   An instant cold pack feels cold as ammonium nitrate dissolves. Is that exothermic or endothermic, Noah?

   • Exothermic: it absorbs heat
   • Endothermic: it absorbs heat
   • Exothermic: it feels cold
8. 7.

   Methane burns in a gas stove's flame. Is that exothermic or endothermic, Pia?

   • Exothermic
   • Neither one
   • Endothermic
9. 8.

   Forming liquid water from hydrogen and oxygen has ΔH = −286 kJ. What does the minus sign mean, Ren?

   • Heat is absorbed
   • No heat moves
   • Heat is released
10. 9.

    What sign does ΔH have for an endothermic reaction, Tala?

    • Negative
    • Exactly zero
    • Positive
11. 10.

    Where does the heat from an exothermic reaction go, Zee?

    • Into the surroundings
    • Nowhere: it vanishes
    • Back into the reactants