Intro to Thermo Quiz

Which of the following correctly explains what is occurring in the reaction below?

2 Na_(s) + Cl_2(g) --> 2 NaCl_(s)

• The reaction is endothermic because energy is being released when bonds between Na and Cl₂ are formed.

• The reaction is exothermic because energy is being released when bonds between Na and Cl₂ are formed.

• The reaction is endothermic because energy is being absorbed to transform Cl_2(g) into Cl_(s).

• The reaction is exothermic because energy is being absorbed to transform Cl_2(g) into Cl_(s).

Tags

NGSS.HS-PS1-4

For a classroom demonstration, a chemistry teacher puts samples of two different pure solid powders in a beaker. The teacher places the beaker on a small wooden board with a wet surface, then stirs the contents of the beaker. After a short time the students observe that the bottom of the beaker is frozen to the wood surface. The teacher asks the students to make a claim about the observation and to justify their claims. Which of the following is the best claim and justification based on the students' observation?

• An exothermic chemical change occurred because heat flowed from the contents of the beaker to the room.

• An exothermic physical change occurred because heat flowed from the contents of the beaker and the water on the board to the room.

• An endothermic physical change occurred because the freezing of water is an endothermic process.

• An endothermic chemical change occurred because the temperature of the beaker and the water on the board decreased as heat was absorbed by the reaction.

Tags

NGSS.HS-PS3-4

Which of the following phase changes involves the transfer of heat from the surroundings to the system?

• CH_4(g) --> CH_4(l), because CH₄ molecules in the gas phase must absorb energy in order to move closer together, thereby increasing the intermolecular attractions in the solid state.

• CO_2(g) --> CO_2(s), because CO₂ molecules in the gas phase must absorb energy in order to move closer together, thereby increasing the intermolecular attractions in the liquid state.

• H₂O_(l) --> H₂O_(s), because H₂O molecules in the liquid phase must absorb energy in order to create a crystalline structure with strong intermolecular attractions in the solid state.

• NH_3(l) --> NH_3(g), because NH₃ molecules in the liquid phase must absorb energy in order to overcome their intermolecular attractions and become free gas molecules.

Tags

NGSS.HS-PS3-4

In the spring, blossoms on cherry trees can be damaged when temperatures fall below -2^oC. When the forecast calls for air temperatures to be below -5^oC for a few hours one night, a farmer sprays his blossoming cherry trees with water, claiming that the blossoms will be protected by the water as it freezes. Which of the following is a correct scientific justification for spraying water on the blossoms to protect them from temperatures below -2^oC?

• Water on the blossoms will not freeze unless the air temperature falls significantly below -5^oC.

• Water is a good thermal conductor that transfers heat from the cold air to the blossoms, keeping the blossoms from going below -2^oC.

• The freezing of water is an endothermic process; thus, water that freezes on the blossoms absorbs heat from the atmosphere, which in turn keeps the blossoms above 0^oC.

• The freezing of water is an exothermic process; thus, water that freezes on the blossoms releases heat to keep the blossoms at or above -2^oC.

Tags

NGSS.HS-PS3-4

What type of reaction is being presented in the energy profile shown?

Tags

NGSS.HS-PS1-4

What type of reaction is being presented in the energy profile shown?

Tags

NGSS.HS-PS1-4

Sketch and energy profile for the following reaction:

Step 1: 3 Ag + Al(NO₃)₃ --> 3 AgNO₃ + Al (exo)

Step 2: 2 AgNO₃ --> 2 Ag + O₂ + 2 NO₂ (endo)

Step 3: 2 NO₂ --> 2 NO + O₂ (endo)

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

XY₂ --> X + Y₂

The equation above represents the decomposition of a compound XY₂. The diagram below shows two reaction profiles (path one and path two) for the decomposition XY₂.

Which of the following best describes the flow of heat when 1.0 mol of XY₂ decomposes?

• 50 kJ of heat is transferred to the surroundings.

• 50 kJ of heat is transferred from the surroundings.

• 100 kJ of heat is transferred to the surroundings.

• 100 kJ of heat is transferred from the surroundings.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

Which of the following correctly describes an exothermic reaction?

• Measured temperature of the surroundings would decrease.

• The energy of the products would be higher than the energy of the reactants

• The reaction would result in a +ΔH^o

• The reaction and resulting products would be energetically favorable.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

Which of the following describes an endothermic reaction? (SELECT ALL THAT APPLY)

• The products are energetically favorable

• The ΔH^o would be positive

• The energy of the reactants is less than that of the products

• The heat flows from the system to the surroundings

Tags

NGSS.HS-PS1-4