Thermochemistry Practice

A 100 g sample of metal was heated to 100^oC and then quickly transferred to an insulated container holding 100 g of water at 22^oC. The temperature of the water rose to reach a final temperature of 35^oC. Which of the following can be concluded?

• The metal temperature changed more than the water temperature did; therefore the metal lost more energy than the water gained.

• The metal temperature changed more than the water temperature did but the metal lost the same amount of thermal energy as the water gained.

• The metal temperature changed more than the water temperature did; therefore the heat capacity of the metal must be greater than the heat capacity of the water.

• The final temperature is less than the average starting temperature of the metal and the water; therefore the total energy of the metal and water decreased.

Tags

NGSS.HS-PS3-4

The dissolution of an ionic solute in a polar solvent can be imagined as occurring in three steps, as shown in the figure above. In step 1, the separation between ions in the solute is greatly increased, just as will occur when the solute dissolves in the polar solvent. In step 2, the polar solvent is expanded to make spaces that the ions will occupy. In the last step, the ions are inserted into the spaces in the polar solvent. Which of the following best describes the enthalpy change, ΔH, for each step?

• All three steps are exothermic.

• All three steps are endothermic.

• Steps 1 and 2 are exothermic, and the final step is endothermic.

• Steps 1 and 2 are endothermic, and the final step is exothermic.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

How much heat is released or absorbed when 0.050 mol of Cl₂ (g) is formed from KCl(s)?

• 87.4 kJ is released

• 43.7 kJ is released

• 43.7 kJ is absorbed

• 87.4 kJ is absorbed

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Which of the values for ΔH^o for a process in the table is (are) less than zero (i.e., indicate(s) an exothermic process)?

• z only

• y and z only

• x, y, and z only

• w, x, y, and z

Tags

NGSS.HS-PS1-4

Which of the following statements is true about bond energies in the reaction above?

• The energy absorbed as the bonds in the reactants are broken is greater than the energy released as the bonds in the product are formed.

• The energy released as the bonds in the reactants are broken is greater than the energy absorbed as the bonds in the product are formed.

• The energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed.

• The energy released as the bonds in the reactants are broken is less than the energy absorbed as the bonds in the product are formed.

Tags

NGSS.HS-PS1-4

A 1.0 g sample of a cashew was burned in a calorimeter containing 1000. g of water and the temperature of the water changed from 20.0°C to 25.0°C. In another experiment, a 3.0 g sample of a marshmallow was burned in a calorimeter containing 2000. g of water, and the temperature of the water changed from 25.0°C to 30.0°C. Based on the data, which of the following can be concluded about the energy content for 1.0 g of each of the two substances? (The specific heat of water is 4.2 J/(g⋅°C)).

• The combustion of 1.0 g of cashew releases less energy than the combustion of 1.0 g of marshmallow.

• The combustion of 1.0 g of cashew releases the same amount of energy as the combustion of 1.0 g marshmallow.

• The combustion of 1.0 g of cashew releases more energy than the combustion of 1.0 g of marshmallow.

• No comparison can be made because the two systems started with different masses of food, different masses of water, and different initial temperatures.

Tags

NGSS.HS-PS3-4

The cooling curve above shows how the temperature of a sample varies with time as the sample goes through phase changes. The sample starts as a gas, and heat is removed at a constant rate. At which time does the sample contain the most liquid?

• t₁

• t₂

• t₃

• t₄

• t₅

Tags

NGSS.MS-PS1-4

Based on the information above, what is the enthalpy change for the sublimation of iodine, represented by I₂(s) → I₂ (g)?

• 15 kJ/mol_rxn

• 21 kJ/mol_rxn

• 31 kJ/mol_rxn

• 42 kJ/mol_rxn

• 62 kJ/mol_rxn

Tags

NGSS.HS-PS1-4

Which of the following expressions is equivalent to ΔH^o for the reaction: Cl₂(g) + 2e^- → 2Cl^- (g)

• x + y

• x - y

• x + 2y

Tags

NGSS.HS-PS1-4

A 10. g cube of copper at a temperature T₁ is placed in an insulated cup containing 10. g of water at a temperature T₂. If T₁ > T₂ , which of the following is true of the system when it has attained thermal equilibrium? (The specific heat of copper is 0.385 J/(g·°C) and the specific heat of water is 4.18 J/(g·°C).)

• The temperature of the copper changed more than the temperature of the water.

• The temperature of the water changed more than the temperature of the copper.

• The temperature of the water and the copper changed by the same amount.

• The relative temperature changes of the copper and the water cannot be determined without knowing T₁ and T₂.

Tags

NGSS.HS-PS3-4