Thermodynamics - AP Chem

HCl_(aq)     +       NH_3(aq)          --->         NH₄⁺_(aq)      +      Cl^-_(aq)  

The chemical reaction between HCl_(aq) and NH_3(aq) is represented above. A student combines equimolar amounts of HCl_(aq) and NH_3(aq) both solutions initially at 24⁰C, in a coffee-cup calorimeter. The student observes that the mixture reaches a temperature of 28⁰C. Based on the experimental results, which of the following can be concluded about the reaction?

• It is an endothermic process, because energy is released by the reaction and is gained by the reaction mixture.

• It is an endothermic process, because energy is absorbed by the reaction and is lost from the reaction mixture.

• It is an exothermic process, because energy is released by the reaction and is gained by the reaction mixture.

• It is an exothermic process, because energy is absorbed by the reaction and is lost from the reaction mixture.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

When pellets of NaOH_(s) are added to a flask of water, it is observed that the temperature of the water increases as the pellets dissolve. Which of the following claims about the observed dissolution of NaOH_(s) in water is most accurate?

 

• It is an endothermic process because heat energy is absorbed by the water as the NaOH_(s) dissolves in it.

• It is an endothermic process because heat energy is released by the water as the NaOH_(s) dissolves in it.

• It is an exothermic process because heat energy is absorbed by the water as the NaOH_(s) dissolves in it.

• It is an exothermic process because heat energy is released by the water as the NaOH_(s) dissolves in it.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

NGSS.HS-PS3-4

An advertisement for a commercial hand warmer claims that the hand warmer works because a chemical reaction in the hand warmer draws out the body’s own natural heat, causing a warming effect. Which of the following states the accuracy of the claim in the advertisement and best provides a correct scientific justification of the claim?

• The advertisement’s claim is inaccurate because heat flowing from the hands to the warmer would only happen if the chemical reaction was endothermic, which would cause the hands to feel colder.

• The advertisement’s claim is inaccurate because heat flowing from the hands to the warmer would only happen if the chemical reaction was exothermic, which would cause the hands to feel colder.

• The advertisement’s claim is accurate because heat flowing from the hands to the warmer would only happen if the chemical reaction was endothermic, which would cause the hands to feel warmer.

• The advertisement’s claim is accurate because heat flowing from the hands to the warmer would only happen if the chemical reaction was exothermic, which would cause the hands to feel warmer.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

A student carefully drops a 9.0g solid Zn pellet initially at 50.0⁰C into an insulated cup containing 30.0g of water at 27.8⁰C. The student predicts that the temperature of the water will increase after the pellet is added. Which of the following statements is the best justification for the student’s prediction?

• The metallic bonds between Zn atoms will break when the Zn is exposed to the water molecules, releasing energy that will be absorbed by the water molecules.

• Collisions between the water molecules and the surface of the Zn pellet will result in the transfer of energy, increasing the average kinetic energy of the water molecules.

• The strength of the hydrogen bonds between the water molecules will increase when the Zn pellet is added, decreasing the average kinetic energy of the water molecules.

• Collisions between Zn atoms in the solid will increase in frequency when the Zn is exposed to the water molecules, resulting in the transfer of energy to the surroundings.

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

Two aqueous NaCl solutions of equal volume and concentration were kept in flasks and held at different temperatures. The two solutions were combined in a larger flask. Based on this information, which of the following predictions is correct?

• The average kinetic energy of the particles in the cooler solution will decrease as they collide with the particles from the warmer solution.

• The average kinetic energy of the particles in the cooler solution will increase as they collide with the particles from the warmer solution.

• The particles from the cooler solution and the particles from the warmer solution will reach thermal equilibrium through collisions, at which time the average kinetic energy of the particles in the mixture will be lower than the average kinetic energy that the particles had in the cooler solution.

• The particles from the cooler solution and the particles from the warmer solution will reach thermal equilibrium through collisions, at which time the average kinetic energy of the particles in the mixture will be higher than the average kinetic energy that the particles had in the warmer solution.

Tags

NGSS.HS-PS3-2

NGSS.HS-PS3-4

The table provides data for two CH₃OH_(l) samples. Based on this information, which of the following statements describes what happens when these samples are initially mixed, and why?

• Thermal energy is transferred between the CH₃OH molecules in sample 1 and the CH₃OH molecules in sample 2 because both samples contain the same substance.

• The CH₃OH molecules from sample 2 transfer thermal energy to the CH₃OH molecules from sample 1 through collisions because there are more moles of molecules in sample 2.

• The CH₃OH molecules from sample 1 transfer thermal energy to the CH₃OH molecules from sample 2 through collisions because sample 1 has a higher density.

• The CH₃OH molecules from sample 1 transfer thermal energy to the CH₃OH molecules from sample 2 through collisions because the average kinetic energy of the molecules in sample 1 is greater.

Tags

NGSS.HS-PS3-4

The graph above shows the changes in temperature recorded for the 2.00L of H₂O surrounding a constant-volume container in which a 1.00g sample of benzoic acid was combusted. Assume that heat was not absorbed by the container or lost to the surroundings, that the density of H₂O is 1.00 g/mL, and that the specific heat capacity of H₂O is about 4.2 J/g ⁰C. Based on this information, estimate how much heat was released from the combustion of the benzoic acid sample.

• 0.013 kJ

• 25 kJ

• 180 kJ

• 210 kJ

Tags

NGSS.HS-PS1-4

For an experiment, a 20.0g piece of Al was placed inside an insulated cup filled with 40.0g of H₂O. The data are given in the table above. Assuming no heat is absorbed by the container or the surroundings, which of the following equations provides the correct mathematical relationship for the transfer of heat q between Al and H₂O?

• – q_Al = 10 x q_H2O

• – q_Al = 5 x q_H2O

• – q_Al = 2 x q_H2O

• – q_Al = q_H2O

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

A student dissolves 8.00g of NH₄NO_3(s) in 100.0g of H₂O_(l) in a coffee-cup calorimeter. Based on the initial and final temperatures of the mixture in degrees Celsius shown in the diagram above the laboratory setup, what is the calculated     ΔT    of the water reported to the appropriate number of significant figures?

• -5.500 ⁰C

• -5.50 ⁰C

• -5.5 ⁰C

• -6 ⁰C

Tags

NGSS.HS-PS3-4

Particulate models of the evaporation of liquid water and the condensation of water vapor are shown above. Based on these models, which of the following accurately compares the energy changes associated with each of the phase changes?

• The amount of energy absorbed by one mole of water molecules as they escape the liquid is greater than the amount of energy released by one mole of water molecules as they come together to form a liquid.

• The amount of energy absorbed by one mole of water molecules as they escape the liquid is less than the amount of energy released by one mole of water molecules as they come together to form a liquid.

• The amount of energy absorbed by one mole of water molecules as they escape the liquid is equal to the amount of energy released by one mole of water molecules as they come together to form a liquid.

• The amount of energy absorbed by one mole of water molecules escaping the liquid can be either greater than or less than the amount of energy released by one mole of water molecules as they come together to form a liquid.

Tags

NGSS.HS-PS3-4