9 chemistry questions, please?

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2. Two objects (A and B) of the same temperature are in contact with each other. Which of the following statements is true?

(Points : 3)

Heat transfers from object B to object A, because molecules from B collide with those from A.

Heat transfers from object A to object B, because molecules from A collide with those from B.

Although the molecules collide, no heat transfers because there is no temperature difference between the objects.

No heat transfers, because there are no collisions between the molecules of the objects.

3. Which of the following parameters is measured directly in a coffee-cup calorimeter?

(Points : 3)

pressure

temperature

heat of fusion

kinetic energy

4. What type of substance would be best for use in a cooling system?

(Points : 3)

a solid with a high specific heat

a liquid with a low specific heat

a liquid with a high specific heat

a gas with a low specific heat

5. The reaction 2NO (g) N2 (g) + O2 (g) has a H = 180.5 kJ. How much heat will be required to produce 44.8 L of NO by the reverse reaction?

(Points : 3)

180.5 kJ

301 kJ

322.3 kJ

644 kJ

6. Which of the following statements is true?

(Points : 3)

In an endothermic reaction, the energy of the products is the same as the energy of the reactants.

In an endothermic reaction, the energy of the products is less than the energy of the reactants.

In an exothermic reaction, the energy of the products is less than the energy of the reactants.

In an exothermic reaction, the energy of the products is the same as the energy of the reactants.

7. Which of the following is a correctly written thermochemical equation?

(Points : 3)

NH4Cl NH4+ + Cl

2C8H18 + 25O2 16CO2 + 18H2O, H = 5,471 kJ/mol

C3H8 (g) + O2 (g) CO2 (g) + H2O (l), H = 2,220 kJ/mol

4Fe (s) + 3O2 (g) 2Fe2O3 (s), H = 3,926 kJ

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8. Which of the following is likely to be true about the H for this reaction?

C6H6 (s) C6H6 (l)

(Points : 3)

H = 0

H > 0

H < 0

10. A chemical reaction is carried out in a closed container. The energy absorbed by the chemical reaction is 100 kJ. What is the energy liberated from the air or the walls of the container?

(Points : 3)

25 kJ

50 kJ

75 kJ

100 kJ

11. Which of the following measures thermal energy in an object?

(Points : 3)

temperature

mass

heat

volume

1 Answer

  • Question 2:

    Two objects (A and B) of the same temperature are in contact with each other. Which of the following statements is true?

    Heat always flows from an object at the higher temperature to an object at the lower temperature until both objects are at the same temperature.

    Answer: Although the molecules collide, no heat transfers because there is no temperature difference between the objects.

    Question 3:

    Which of the following parameters is measured directly in a coffee-cup calorimeter?

    As the name indicates, a “calorimeter” is a device for measuring heat. However, heat must be calculated using direct measurements of temperature, and mass.

    “Pressure” is not measured in a calorimeter.

    “Heat of fusion” is not measured directly, but must be calculated based on measured temperature and mass of a substance.

    “Kinetic energy” is not measured directly.

    Answer: “Temperature” is directly measured in a calorimeter.

    Question 4: What type of substance would be best for use in a cooling system?

    Answer: a liquid with a high specific heat

    The reason for the above is that a liquid with a high specific heat would absorb a great deal of heat for every degree Celsius of temperature increase, so it would not heat up too quickly, and be able to lower the temperature of whatever needed cooling.

    Question 5:

    The reaction 2 NO(g) → N2(g) + O2(g) has a ΔH = 180.5 kJ. How much heat will be required to produce 44.8 L of NO by the reverse reaction?

    Since ΔH appears to be positive, I assume that the forward reaction is endothermic, and the heat term should appear on the left side of the equation:

    2 NO(g) + 180.5 kJ → N2(g) + O2(g)

    Since 1 mole of any gas at STP occupies 22.4 L of volume, 44.8 L represents two moles of NO, as indicated in the equation. Therefore 180.5 kJ of heat will be released by the reverse reaction when 44.8 L of NO is produced.

    Answer: 180.5 kJ

    question 6:

    Which of the following statements is true?

    “In an endothermic reaction, the energy of the products is the same as the energy of the reactants.”

    The above statement is false, because, due to absorption of energy, the energy of the products is greater than the energy of reactants.

    “In an endothermic reaction, the energy of the products is less than the energy of the reactants.”

    The above statement is false because, due to absorption of energy, the energy of the products is greater than the energy of reactants.

    “In an exothermic reaction, the energy of the products is less than the energy of the reactants.”

    The above statement is true, because reactants lose energy to become products.

    “In an exothermic reaction, the energy of the products is the same as the energy of the reactants.”

    The above statement is false, because reactants lose energy to become products, so the energy of the products is is less than the energy of the reactants.

    Question 7:

    Which of the following is a correctly written thermochemical equation?

    NH4Cl → NH4+ + Cl

    The above equation does not provide any information about thermal energy changes and the last term should show negative charge.

    2 C8H18 + 25 O2 → 16 CO2 + 18 H2O, ΔH = 5,471 kJ/mol

    The above equation is a typical combustion reaction. Combustion is an exothermic change, so ΔH must be negative.

    C3H8(g) + O2(g) → CO2(g) + H2O(l), ΔH = 2,220 kJ/mol

    The above combustion equation is not balanced, and ΔH should be negative.

    4 Fe(s) + 3 O2(g) → 2 Fe2O3(s), ΔH = 3,926 kJ

    The above combustion equation should have a negative ΔH.

    Note: None of the equations seems to be written correctly.

    Question 8:

    Which of the following is likely to be true about the ΔH for this reaction?

    C6H6(s) → C6H6(l)

    Melting of a solid is an endothermic change, so ΔH for this reaction is positive.

    Answer: H > 0

    Question 10:

    A chemical reaction is carried out in a closed container. The energy absorbed by the chemical reaction is 100 kJ. What is the energy liberated from the air or the walls of the container?

    The law of conservation of energy states that energy cannot be created or destroyed, but only changed from one form into another. When a chemical reaction absorbs a certain amount of heat, the surroundings must lose (liberate) the same amount of heat as well.

    Answer: 100 kJ

    Question 11:

    Which of the following measures thermal energy in an object?

    Temperature is proportional to the average kinetic energy of the molecules of an object.

    Mass is the amount of matter in an object.

    Heat is a form of energy, sometimes called “thermal” energy.

    Volume is the amount of space an object takes up.

    Answer: heat

    Note: If you want me to answer any more of your questions, please limit them to one or two at a time. Please read the explanations so you understand the concepts involved. Just copying answers will not help you pass your exams.

    Source(s): personal knowledge


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