AP Chem Thermodynamics

Thermochemistry is small portion of thermodynamics, which is studying how energy changes during a chemical reaction. Some reactions will absorb heat, while others will release it, and can do work.

Complete this fundamental principle of thermochem:

Energy is _____ when chemical bonds are formed; energy is _____ when chemical bonds are broken.

• consumed / released

• released / consumed

The endothermic process among the following is

• Natural gas is combusted in a Bunsen burner.

• Water vapor condenses on the outside of a glass of iced tea.

• A cop of hot water cools as a tea bag brews.

• An ice cube melts on a countertop.

The enthalpy change for 2Na + Cl₂ --> 2NaCl is -35 kJ. What is the heat of reaction for 2NaCl --> 2Na + Cl₂

• - 35 kJ

• 35 kJ

• 70 kJ

• - 70 kJ

The heat of reaction for 2H₂ + O₂ --> 2H₂O is -40 kJ. What is the heat of reaction for H₂O --> H₂ + 1/2 O₂?

• - 40 kJ

• 20 kJ

• - 80 kJ

• 80 kJ

2H₂O + 25 kJ --> 2H₂ + O₂ How much energy is absorbed when 36 grams of water is decomposed?

• 25 kJ

• 50 kJ

• 12.5 kJ

• 900 kJ

What is the standard enthalpy change for the following reaction?

2 CO + O₂ -> 2 CO₂

•ΔH of CO₂ = -394 kJ/mol

•ΔH of CO = -110 kJ/mol

_{(try without a calculator)}

• -504 kJ/mol

• +568 kJ/mol

• +284 kJ/mol

• -284 kJ/mol

• -568 kJ/mol

Find the enthalpy change ΔH for the following reactions using the info from the table

N₂ + 3H₂ --> 2NH₃

_{(Try without a calculator)}

• +109 kJ/mol

• +151 kJ/mol

• +982 kJ/mol

• -151 kJ/mol

• -109 kJ/mol

4P + 3O₂ --> P₄O₆ ΔH = -1640 kJ/mol

2P₄O₁₀ --> 2P₄O₆ + 4O₂ ΔH = -2688 kJ/mol

Use the above info to find the enthalpy change for the following reaction:

4P + 5O₂ --> P₄O₁₀

_{(try without a calculator)}

• -4328 kJ/mol

• +3028 kJ/mol

• -296 kJ/mol

• +296 kJ/mol

• +3028 kJ/mol

This reaction is most likely

• endothermic.

• exothermic.

H₂ + 2 C + N₂ + 270.3 kJ --> 2 HCN
Is this reaction endothermic or exothermic?

• Endothermic 
• Exothermic