AP Chemistry 6.5-6.5 Knowledge Check

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 of 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

In an insulated cup of negligible heat capacity, 50. g of water at 40.0°C is mixed with 30. g of water at 20.0°C. The final temperature of the mixture is closest to

• 22°C

• 27°C

• 30°C

• 33°C

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

A molecular solid coexists with its liquid phase at its melting point. The solid-liquid mixture is heated, but the temperature does not change while the solid is melting. The best explanation for this phenomenon is that the heat absorbed by the mixture

• is lost to the surroundings very quickly

• is used in overcoming the intermolecular attractions in the solid

• is used in breaking the bonds within the molecules of the solid

• causes the nonbonding electrons in the molecules to move to lower energy levels

Tags

NGSS.HS-PS3-4

A 2.00 mol sample of C₂H₅OH undergoes the phase transition illustrated in the diagram at left. The molar enthalpy of vaporization, ΔH_vap, of C₂H₅OH is +38.6 kJ/mol. Which of the following best identifies the change in enthalpy in the phase transition shown in the diagram?

• A. +19.3kJ

• B. +77.2kJ

• C. −19.3kJ

• D. −77.2kJ

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

How much energy is required to melt 64 g of methane at 90 K? (The molar mass of methane is 16 g/mol.)

• 0.24 kJ

• 3.8 kJ

• 33 kJ

• 60. 60 kJ

Tags

NGSS.HS-PS3-4

2 H2S(g) + 3 O2(g) ⟶ 2 H2O(l) + 2 SO2(g)          ΔH° = － 1120 kJ/molrxn

Based on the reaction represented by the chemical equation shown above, what is the amount of heat released when 4.00 mol of H2S(g) reacts with 9.00 mol of O2(g)?

• -560 kJ

• -1120kJ

• -2240kJ

• -3360kJ

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Mg(s) + 2 HCl(aq) ⟶ MgCl2(aq) + H2(g)

The chemical equation shown above represents the reaction between Mg(s) and HCl(aq). When 12.15 g of Mg(s) is added to 500.0mL of 4.0M HCl(aq), 95 kJ of heat is released. The experiment is repeated with 24.30 g of Mg(s) and 500.0 mL of 4.0M HCl(aq). Which of the following gives the correct value for the amount of heat released by the reaction?

• 380 kJ

• 190 kJ

• 95 kJ

• 48 kJ

Tags

NGSS.HS-PS1-4