Bond Enthalpies

Multiple Choice

Which is an example of an endothermic physical reaction? 

• a) Ice melting 
• b) Combustion 
• c) Steam condensing 
• d) Photosynthesis

Multiple Choice

Does breaking bonds require energy, release energy, or not involve energy at all?

• requires energy to break

• releases energy when broken

• No energy involved

Multiple Choice

What kind of energy change happens in the photosynthesis reaction in plant leaves?

• Endothermic

• Exothermic

• No change

Multiple Choice

Is this equation endo- or exo-thermic?

PCl3 (s) + Cl2 (g) --> PCl5 (s) + energy

• endothermic

• exothermic

Multiple Choice

Is this equation endo- or exo-thermic?

2KNO3 (s) + energy --> 2KNO2 (s) + O2

• endothermic

• exothermic

Multiple Choice

How can we figure out if an overall reaction is endo- or exo-thermic? It is the difference between _______ and __________.

• hot and cold temperatures

• energy to break and energy to form bonds.

• time to form a bond versus time to break a bond

Multiple Choice

For the reaction 2H₂(g) + O₂(g) → 2H₂O(g) the bond enthalpies (in kJ/mol) are

H-H = x, O=O = y, O-H = z

Which calculation will give the value, in kJ/mol, of ΔH for the reaction?

• 2x + y - 2z

• 4z - 2x - y

• 2x + y - 4z

• 2z - 2x - y