Calculate energy changes from bond energies

Question 1

H₂ + Cl₂ → 2HCl. Bond energies (kJ/mol): H–H 436, Cl–Cl 243, H–Cl 432. Calculate the energy change, in kJ/mol.

Answer kJ/mol

Question 2

Why is breaking bonds endothermic?

• A. Energy must be supplied to overcome the attraction holding atoms together
• B. Breaking bonds releases heat
• C. Atoms repel each other
• D. Bonds contain no energy

Question 3

In a reaction, 1350 kJ is needed to break bonds and 1200 kJ is released when new bonds form. Is the reaction exothermic or endothermic?

• A. exothermic
• B. endothermic

Question 4

CH₄ + 2O₂ → CO₂ + 2H₂O. Bond energies (kJ/mol): C–H 413, O=O 498, C=O 805, O–H 464. Calculate the energy change, in kJ/mol.

Answer kJ/mol

Question 5

Why is breaking bonds endothermic?

• A. Bonds contain no energy
• B. Atoms repel each other
• C. Breaking bonds releases heat
• D. Energy must be supplied to overcome the attraction holding atoms together

Question 6

In a reaction, 900 kJ is needed to break bonds and 1020 kJ is released when new bonds form. Is the reaction exothermic or endothermic?

• A. exothermic
• B. endothermic

Question 7

H₂ + Cl₂ → 2HCl. Bond energies (kJ/mol): H–H 436, Cl–Cl 243, H–Cl 432. Calculate the energy change, in kJ/mol.

Answer kJ/mol

Question 8

Why is breaking bonds endothermic?

• A. Bonds contain no energy
• B. Breaking bonds releases heat
• C. Energy must be supplied to overcome the attraction holding atoms together
• D. Atoms repel each other

Question 9

In a reaction, 1350 kJ is needed to break bonds and 1600 kJ is released when new bonds form. Is the reaction exothermic or endothermic?

• A. exothermic
• B. endothermic

Question 10

CH₄ + 2O₂ → CO₂ + 2H₂O. Bond energies (kJ/mol): C–H 413, O=O 498, C=O 805, O–H 464. Calculate the energy change, in kJ/mol.

Answer kJ/mol

Question 11

Why is breaking bonds endothermic?

• A. Bonds contain no energy
• B. Energy must be supplied to overcome the attraction holding atoms together
• C. Atoms repel each other
• D. Breaking bonds releases heat

Question 12

In a reaction, 1300 kJ is needed to break bonds and 1000 kJ is released when new bonds form. Is the reaction exothermic or endothermic?

• A. exothermic
• B. endothermic

Question 13

CH₄ + 2O₂ → CO₂ + 2H₂O. Bond energies (kJ/mol): C–H 413, O=O 498, C=O 805, O–H 464. Calculate the energy change, in kJ/mol.

Answer kJ/mol

Question 14

Hydrogen fuel cells combine hydrogen and oxygen. Why do they release energy overall?

• A. More energy is released forming O–H bonds than is needed to break H–H and O=O
• B. Water absorbs energy
• C. Hydrogen is radioactive
• D. No bonds are broken

Question 15

In a reaction, 1450 kJ is needed to break bonds and 1700 kJ is released when new bonds form. Is the reaction exothermic or endothermic?

• A. exothermic
• B. endothermic

Question 16

N₂ + 3H₂ → 2NH₃. Bond energies (kJ/mol): N≡N 945, H–H 436, N–H 391. Calculate the energy change, in kJ/mol.

Answer kJ/mol