Chemistry SE 11 C

1.

Which of the following equations is an exothermic reaction?

H2 (g) + ½ O2 (g) → H2O (l)ΔH = -285.8 kJ

HgO (s) → Hg (l) + ½ O2 (g)ΔH = +90.7 kJ

4CO2(g) +6H2O(l) →2C2H6(g) +7O2(g)ΔH =+3120 kJ

SO2 (g) → S(s)+ O2 (g)ΔH = +296 kJ

The reaction H2 (g) + ½ O2 (g) → H2O (l) with a ΔH of -285.8 kJ is an exothermic reaction because the enthalpy change is negative. In an exothermic reaction, energy is released in the form of heat, resulting in a decrease in enthalpy.

Explanation

The reaction H2 (g) + ½ O2 (g) → H2O (l) with a ΔH of -285.8 kJ is an exothermic reaction because the enthalpy change is negative. In an exothermic reaction, energy is released in the form of heat, resulting in a decrease in enthalpy.

2.

What is the term for the amount of energy absorbed or released in a chemical reaction?

Heat of reaction

Heat of vaporization

Heat of condensation

Heat of sublimation

The term for the amount of energy absorbed or released in a chemical reaction is called the heat of reaction. This term refers to the heat energy that is either absorbed from the surroundings or released to the surroundings during a chemical reaction. It is a measure of the change in energy of the system as a result of the reaction.

Explanation

The term for the amount of energy absorbed or released in a chemical reaction is called the heat of reaction. This term refers to the heat energy that is either absorbed from the surroundings or released to the surroundings during a chemical reaction. It is a measure of the change in energy of the system as a result of the reaction.

3.

A change in the internal energy of a system at constant pressure from a chemical reaction will result in an identical change in the —

Enthalpy of the system

Entropy of the system

Free energy of the system

Specific heat of the system

A change in the internal energy of a system at constant pressure from a chemical reaction will result in an identical change in the enthalpy of the system. Enthalpy is defined as the heat absorbed or released by a system at constant pressure, and it is directly related to the internal energy of the system. Therefore, any change in the internal energy of the system will result in an identical change in the enthalpy of the system.

Explanation

A change in the internal energy of a system at constant pressure from a chemical reaction will result in an identical change in the enthalpy of the system. Enthalpy is defined as the heat absorbed or released by a system at constant pressure, and it is directly related to the internal energy of the system. Therefore, any change in the internal energy of the system will result in an identical change in the enthalpy of the system.

4.

Which of the following applies to an exothermic reaction?

Hfinal < Hinitial ∆H < 0

Hfinal < Hinitial ∆H > 0

Hfinal > Hinitial ∆H > 0

Hfinal > Hinitial ∆H < 0

An exothermic reaction is a reaction that releases heat to its surroundings. In this case, the final enthalpy (Hfinal) is less than the initial enthalpy (Hinitial), indicating that the reaction has released heat. The symbol ∆H represents the change in enthalpy, and since the reaction is exothermic, ∆H is negative, indicating a decrease in enthalpy. Therefore, the correct answer is Hfinal

Explanation

An exothermic reaction is a reaction that releases heat to its surroundings. In this case, the final enthalpy (Hfinal) is less than the initial enthalpy (Hinitial), indicating that the reaction has released heat. The symbol ∆H represents the change in enthalpy, and since the reaction is exothermic, ∆H is negative, indicating a decrease in enthalpy. Therefore, the correct answer is Hfinal

5. 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.

The rapid drop in water temperature suggests that heat energy was absorbed from the water by the compound, indicating an endothermic reaction.

Explanation

The rapid drop in water temperature suggests that heat energy was absorbed from the water by the compound, indicating an endothermic reaction.

6.

The table below shows the standard enthalpy of formation for each of three substances.

CaCO decomposes according to the equation CaCO3 (s) --> CaO(s) + CO2 (g). What is the
enthalpy of reaction?

177.8 kJ

-177.8 kJ

−1029 kJ

−2236 kJ

The enthalpy of reaction can be calculated by subtracting the sum of the enthalpies of formation of the reactants from the sum of the enthalpies of formation of the products. In this case, the enthalpy of formation of CaCO3 is not given, but we can assume it to be zero since it is the most stable form of calcium carbonate. The enthalpy of formation of CaO is -635.1 kJ/mol and the enthalpy of formation of CO2 is -393.5 kJ/mol. Therefore, the enthalpy of reaction is (-635.1 kJ/mol) - (0 kJ/mol) - (-393.5 kJ/mol) = 241.6 kJ/mol. Since the equation has a coefficient of 1 for CaCO3, the enthalpy of reaction is 241.6 kJ. Therefore, the correct answer is 177.8 kJ.

Explanation

The enthalpy of reaction can be calculated by subtracting the sum of the enthalpies of formation of the reactants from the sum of the enthalpies of formation of the products. In this case, the enthalpy of formation of CaCO3 is not given, but we can assume it to be zero since it is the most stable form of calcium carbonate. The enthalpy of formation of CaO is -635.1 kJ/mol and the enthalpy of formation of CO2 is -393.5 kJ/mol. Therefore, the enthalpy of reaction is (-635.1 kJ/mol) - (0 kJ/mol) - (-393.5 kJ/mol) = 241.6 kJ/mol. Since the equation has a coefficient of 1 for CaCO3, the enthalpy of reaction is 241.6 kJ. Therefore, the correct answer is 177.8 kJ.

Chemistry Se 11 C