TEKS 11C , 11D

11C-Exo-Endo (#1)

A sample of a compound is added to distilled water in a clean beaker. A reaction occurs, and the water

temperature increases rapidly. What type of reaction occurred?

• Exothermic

• Endothermic

11C. Exo-Endo (#2)

Solid A and solid B were dissolved in two separate graduated cylinders, each containing 270 mL of water. (Refer to the diagram in your questionnaire). Which statement best describes the dissolving reactions of solid A and solid B?

• The dissolving reactions of both A and B were endothermic.

• The dissolving reactions of both A and B were exothermic.

• The dissolving reaction of A was exothermic, and the dissolving reaction of B was endothermic.

• The dissolving reaction of A was endothermic, and the dissolving reaction of B was exothermic.

11C. Exo-Endo (#3)

The formation reaction for nitrogen oxide gas is at follows: the change in enthalpy is 181 kJ/mole.

N₂ (g) + O₂ (g) --> 2 NO (g)

The reaction would be considered__

• Endothermic with release of heat.

• Endothermic with an absorption of heat.

• Exothermic with release of heat.

• Exothermic with an absorption of heat.

11C. Exo-Endo (#4)

A sample of a compound is added to distilled water in a clean beaker. A reaction occurs, and the water temperature

drops rapidly. Which of the following statements is best supported by this observation?

• An endothermic reaction occurred.

• A dehydration reaction occurred.

• The water was originally warmer than the compound.

• The beaker was contaminated by another compound.

11C. Exo-Endo (#5)

Which of the following best describes this reaction?

N₂ (g) + O₂ (g) --> 2 NH₃ (g) + heat

• Endothermic with release of heat

• Exothermic with release of heat

• Endothermic with an absorption of heat

• Exothermic with an absorption of heat

11C. Standard HOF (#1)

When vinegar and baking soda are combined, a chemical reaction occurs and there is a change in enthalpy. An energy graph of this reaction is provided in your questionnaire. What type of reaction and energy change occurred?

• exothermic, + ΔH

• exothermic, - ΔH

• endothermic, + ΔH

• endothermic, - ΔH

11C Standard HOF (#2)

Below is a double replacement reaction. What is the change in enthalpy of the reaction?

AgNO₃ + NaCl --> AgCl + NaNO₃

Compound ΔH_f^o kJ/mole

AgCl -127.0

NaCl -411.0

AgNO₃ -123.02

NaNO₃ -446.12

• -39.1 kJ

• +1107.14 kJ

• 39.1 kJ

• -1107.14 kJ

11C. Standard HOF (#3)

Calculate the heat of combustion of C₂H_6. The heats of formation are as follows: ∆H_f° (C₂H₆ (g)) = -84.5

kJ/mol, ∆H_f° (CO₂ (g)) = -110.5 kJ/mol, ∆H_f° (H₂O (l)) = -286 kJ/mol. Determine whether this reaction is endothermic or exothermic.

2C₂H₆ (g) + 7 O₂ (g) à 4CO₂ (g) + 6H₂O (l)

• 2327 kJ, endothermic

• -312 kJ, exothermic

• -1989 kJ, exothermic

• +422.5 kJ, endothermic

11C. Standard HOF (#4)

Calculate the heat of formation for the decomposition of two moles of water according to the following endothermic reaction, using the table to the left.

2H₂O (g) --> 2H₂ (g) + O₂ (g)

• 483.6 kJ

• -483.6 kJ

• 241.8 kJ

• -241.3 kJ

11C. Hess' (#1)

The enthalpy change for the reaction:

C(s) _graphite + 1/2 O₂ (g) --> CO (g)

cannot be measured directly since some carbon dioxide is always formed in the reaction. Using Hess' law, calculate the enthalpy changes of for the reaction of graphite.

C(s) _graphite + O₂ (g) --> CO₂ (g)

CO (g) + 1/2 O₂ (g) --> CO₂ (g)

• -677 kJ/mole

• -111 kJ/mole

• +111 kJ/mole

• +677 kJ/mole