A Unique Quiz On Thermochemistry

1. The SI unit of energy is

Heat capacity.

Calorie.

Joule.

Enthalpy.

The SI unit of energy is joule. Joule is the standard unit of energy in the International System of Units (SI). It is defined as the amount of work done when a force of one newton is applied over a distance of one meter. This unit is commonly used to measure energy in various fields such as physics and engineering. Heat capacity, calorie, and enthalpy are not SI units of energy.

Explanation

The SI unit of energy is joule. Joule is the standard unit of energy in the International System of Units (SI). It is defined as the amount of work done when a force of one newton is applied over a distance of one meter. This unit is commonly used to measure energy in various fields such as physics and engineering. Heat capacity, calorie, and enthalpy are not SI units of energy.

2. The temperature of a 6.0-g sample of glass changed from 20C to 45C when it absorbed 550 J of heat. What is the specific heat of this glass sample?

C0.27 J/gpC

3.7 J/gp

2300 J/gpC

The specific heat of a substance is the amount of heat energy required to raise the temperature of 1 gram of that substance by 1 degree Celsius. In this question, the glass sample absorbed 550 J of heat and its temperature changed by 25 degrees Celsius. To find the specific heat, we can use the formula Q = mcΔT, where Q is the heat energy absorbed, m is the mass of the substance, c is the specific heat, and ΔT is the change in temperature. Rearranging the formula, we have c = Q / (m * ΔT). Plugging in the values, c = 550 J / (6.0 g * 25 °C) = 3.7 J/g°C. Therefore, the specific heat of the glass sample is 3.7 J/g°C.

Explanation

The specific heat of a substance is the amount of heat energy required to raise the temperature of 1 gram of that substance by 1 degree Celsius. In this question, the glass sample absorbed 550 J of heat and its temperature changed by 25 degrees Celsius. To find the specific heat, we can use the formula Q = mcΔT, where Q is the heat energy absorbed, m is the mass of the substance, c is the specific heat, and ΔT is the change in temperature. Rearranging the formula, we have c = Q / (m * ΔT). Plugging in the values, c = 550 J / (6.0 g * 25 °C) = 3.7 J/g°C. Therefore, the specific heat of the glass sample is 3.7 J/g°C.

3. When your body is warmed by an electric blanket during the winter, this process is said to be

Endothermic.

Exothermic.

Isothermic.

When your body is warmed by an electric blanket during the winter, it is considered endothermic because the blanket is providing heat to your body, causing your body temperature to increase. Endothermic refers to a process or reaction that absorbs heat from its surroundings. In this case, the electric blanket absorbs heat from its source (electricity) and transfers it to your body, resulting in warming.

Explanation

When your body is warmed by an electric blanket during the winter, it is considered endothermic because the blanket is providing heat to your body, causing your body temperature to increase. Endothermic refers to a process or reaction that absorbs heat from its surroundings. In this case, the electric blanket absorbs heat from its source (electricity) and transfers it to your body, resulting in warming.

4. How many calories are required to raise the temperature of 75.0 g of water from 20C to 50C?

2250 cal

3750 cal

75.0 cal

To calculate the calories required to raise the temperature of water, we can use the formula: Q = mcΔT, where Q is the heat energy, m is the mass of water, c is the specific heat capacity of water, and ΔT is the change in temperature. Given that the mass of water is 75.0 g and the change in temperature is 50°C - 20°C = 30°C, we can substitute these values into the formula. The specific heat capacity of water is approximately 1 cal/g°C. Therefore, Q = (75.0 g)(1 cal/g°C)(30°C) = 2250 cal. Hence, 2250 cal is the correct answer.

Explanation

To calculate the calories required to raise the temperature of water, we can use the formula: Q = mcΔT, where Q is the heat energy, m is the mass of water, c is the specific heat capacity of water, and ΔT is the change in temperature. Given that the mass of water is 75.0 g and the change in temperature is 50°C - 20°C = 30°C, we can substitute these values into the formula. The specific heat capacity of water is approximately 1 cal/g°C. Therefore, Q = (75.0 g)(1 cal/g°C)(30°C) = 2250 cal. Hence, 2250 cal is the correct answer.

5. If 1 Calorie 4.18 kJ, how many kJ of energy can be released by an apple containing 125 Cal?

522 kJ

29.9 kJ

5.22 105 kJ

An apple containing 125 Calories can release 522 kJ of energy. This is because 1 Calorie is equivalent to 4.18 kJ. By multiplying 125 Calories by 4.18 kJ, we can calculate that the apple can release a total of 522 kJ of energy.

Explanation

An apple containing 125 Calories can release 522 kJ of energy. This is because 1 Calorie is equivalent to 4.18 kJ. By multiplying 125 Calories by 4.18 kJ, we can calculate that the apple can release a total of 522 kJ of energy.

6. How much heat is required to convert 9.00 g of water at 100C into steam at 100C, if ^Hvap for water = 40.7 kJ/mol?

20.4 kJ

366 kJ

18.0 kJ

The heat required to convert a substance from one phase to another is given by the formula Q = m * ΔH, where Q is the heat, m is the mass, and ΔH is the enthalpy change. In this case, we are converting water at 100C into steam at 100C. The enthalpy change for vaporization of water is given as 40.7 kJ/mol. We are given the mass of water as 9.00 g. To find the heat required, we need to convert the mass to moles by dividing by the molar mass of water, which is approximately 18 g/mol. So, 9.00 g / 18 g/mol = 0.50 mol. Now we can calculate the heat using Q = 0.50 mol * 40.7 kJ/mol = 20.4 kJ. Therefore, the correct answer is 20.4 kJ.

Explanation

The heat required to convert a substance from one phase to another is given by the formula Q = m * ΔH, where Q is the heat, m is the mass, and ΔH is the enthalpy change. In this case, we are converting water at 100C into steam at 100C. The enthalpy change for vaporization of water is given as 40.7 kJ/mol. We are given the mass of water as 9.00 g. To find the heat required, we need to convert the mass to moles by dividing by the molar mass of water, which is approximately 18 g/mol. So, 9.00 g / 18 g/mol = 0.50 mol. Now we can calculate the heat using Q = 0.50 mol * 40.7 kJ/mol = 20.4 kJ. Therefore, the correct answer is 20.4 kJ.

7. Given the equation Si(s) + 2Cl2(g) ------>SiCl2(g) ------>SiCl2(l) + 687 kJ, how much heat is produced when 106 g of Cl2 react?

513 kJ

360 kJ

180 kJ

In this chemical reaction, 1 mole of Si reacts with 2 moles of Cl2 to produce 1 mole of SiCl2. The given equation states that 687 kJ of heat is produced in this reaction. To find the amount of heat produced when 106 g of Cl2 react, we need to convert the mass of Cl2 to moles. The molar mass of Cl2 is 70.90 g/mol, so 106 g of Cl2 is equal to 1.49 moles. Since the reaction ratio is 2 moles of Cl2 to 687 kJ of heat, we can set up a proportion to find the amount of heat produced when 1.49 moles of Cl2 react. Solving the proportion, we find that the amount of heat produced is approximately 513 kJ.

Explanation

In this chemical reaction, 1 mole of Si reacts with 2 moles of Cl2 to produce 1 mole of SiCl2. The given equation states that 687 kJ of heat is produced in this reaction. To find the amount of heat produced when 106 g of Cl2 react, we need to convert the mass of Cl2 to moles. The molar mass of Cl2 is 70.90 g/mol, so 106 g of Cl2 is equal to 1.49 moles. Since the reaction ratio is 2 moles of Cl2 to 687 kJ of heat, we can set up a proportion to find the amount of heat produced when 1.49 moles of Cl2 react. Solving the proportion, we find that the amount of heat produced is approximately 513 kJ.

8. The enthalpy of a system is the same as its:

Specific heat.

Heat of combustion.

Heat content.

The enthalpy of a system refers to the total heat content of the system, including both the internal energy and the work done by or on the system. It is a measure of the energy stored within the system, and is independent of the system's mass or size. Specific heat, on the other hand, is the amount of heat required to raise the temperature of a unit mass of a substance by a certain amount. Heat of combustion is the amount of heat released during a combustion reaction. Therefore, the correct answer is "heat content" as it encompasses the total energy stored within the system.

Explanation

The enthalpy of a system refers to the total heat content of the system, including both the internal energy and the work done by or on the system. It is a measure of the energy stored within the system, and is independent of the system's mass or size. Specific heat, on the other hand, is the amount of heat required to raise the temperature of a unit mass of a substance by a certain amount. Heat of combustion is the amount of heat released during a combustion reaction. Therefore, the correct answer is "heat content" as it encompasses the total energy stored within the system.

9. Which of the following statements is true?

^Hfus^Hsolid

^Hsolid is always positive.

This statement is true because the symbol "^H" represents the enthalpy change, and in this case, it refers to the enthalpy of fusion (Hfus) and the enthalpy of solidification (Hsolid). The "^Hfus" symbol followed by "^Hsolid" indicates that the enthalpy change of fusion is equal in magnitude but opposite in sign to the enthalpy change of solidification. This means that when a substance melts (undergoes fusion), it absorbs a certain amount of heat energy, and when it solidifies, it releases the same amount of heat energy. Therefore, the enthalpy change of fusion is equal to the negative of the enthalpy change of solidification.

Explanation

This statement is true because the symbol "^H" represents the enthalpy change, and in this case, it refers to the enthalpy of fusion (Hfus) and the enthalpy of solidification (Hsolid). The "^Hfus" symbol followed by "^Hsolid" indicates that the enthalpy change of fusion is equal in magnitude but opposite in sign to the enthalpy change of solidification. This means that when a substance melts (undergoes fusion), it absorbs a certain amount of heat energy, and when it solidifies, it releases the same amount of heat energy. Therefore, the enthalpy change of fusion is equal to the negative of the enthalpy change of solidification.

10. If the molar heat of solution of NH4NO3 is 25.7 kJ/mol, how much heat (in kJ) would be required to dissolve 20.0 g of NH4NO3 in water?

0.250 kJ

514 kJ

6.43 kJ

The molar heat of solution of NH4NO3 is given as 25.7 kJ/mol. To calculate the heat required to dissolve 20.0 g of NH4NO3 in water, we need to convert the mass of NH4NO3 to moles. The molar mass of NH4NO3 is 80.04 g/mol. Therefore, the number of moles of NH4NO3 is 20.0 g / 80.04 g/mol = 0.2499 mol. Finally, we can calculate the heat required using the formula: heat = molar heat of solution * number of moles = 25.7 kJ/mol * 0.2499 mol = 6.43 kJ.

Explanation

The molar heat of solution of NH4NO3 is given as 25.7 kJ/mol. To calculate the heat required to dissolve 20.0 g of NH4NO3 in water, we need to convert the mass of NH4NO3 to moles. The molar mass of NH4NO3 is 80.04 g/mol. Therefore, the number of moles of NH4NO3 is 20.0 g / 80.04 g/mol = 0.2499 mol. Finally, we can calculate the heat required using the formula: heat = molar heat of solution * number of moles = 25.7 kJ/mol * 0.2499 mol = 6.43 kJ.

11. Given the equation 2Mg(s) O2(g) y2MgO(s) 72.3 kJ, which of the following is true?

The reaction is endothermic.

^H72.3 kJ

The given equation shows the formation of 2 moles of MgO from 2 moles of Mg and 1 mole of O2. The value of ^H (enthalpy change) is +72.3 kJ, indicating that the reaction absorbs energy from the surroundings. This means that the reaction is endothermic, as it requires an input of energy to occur.

Explanation

The given equation shows the formation of 2 moles of MgO from 2 moles of Mg and 1 mole of O2. The value of ^H (enthalpy change) is +72.3 kJ, indicating that the reaction absorbs energy from the surroundings. This means that the reaction is endothermic, as it requires an input of energy to occur.

12. How much heat, in kJ, is required to melt 54.0 g of ice at 0C into water at 0C if ^Hfus for water = 6.01 kJ/mol?

0.111 kJ

325 kJ

18.0 kJ

The correct answer is 18.0 kJ because to calculate the heat required to melt the ice, we need to use the formula Q = m * ^Hfus, where Q is the heat, m is the mass of the ice, and ^Hfus is the enthalpy of fusion. Plugging in the values, we get Q = 54.0 g * (6.01 kJ/mol / 18.0 g/mol) = 18.0 kJ.

Explanation

The correct answer is 18.0 kJ because to calculate the heat required to melt the ice, we need to use the formula Q = m * ^Hfus, where Q is the heat, m is the mass of the ice, and ^Hfus is the enthalpy of fusion. Plugging in the values, we get Q = 54.0 g * (6.01 kJ/mol / 18.0 g/mol) = 18.0 kJ.

13. A student mixes two water solutions with an initial temperature of 25.0C to form a final solution with a mass of 65.0 g at 30.0C. What is the heat change, in kJ, for this reaction?

325 kJ

272 kJ

1.36 kJ

The heat change for a reaction can be calculated using the equation Q = mcΔT, where Q is the heat change, m is the mass of the solution, c is the specific heat capacity of water, and ΔT is the change in temperature. In this case, the mass of the final solution is given as 65.0 g and the change in temperature is 30.0C - 25.0C = 5.0C. The specific heat capacity of water is approximately 4.18 J/g°C. Plugging these values into the equation, we get Q = (65.0 g)(4.18 J/g°C)(5.0C) = 1361 J. Converting this to kJ, we get 1.36 kJ. Therefore, the heat change for this reaction is 1.36 kJ.

Explanation

The heat change for a reaction can be calculated using the equation Q = mcΔT, where Q is the heat change, m is the mass of the solution, c is the specific heat capacity of water, and ΔT is the change in temperature. In this case, the mass of the final solution is given as 65.0 g and the change in temperature is 30.0C - 25.0C = 5.0C. The specific heat capacity of water is approximately 4.18 J/g°C. Plugging these values into the equation, we get Q = (65.0 g)(4.18 J/g°C)(5.0C) = 1361 J. Converting this to kJ, we get 1.36 kJ. Therefore, the heat change for this reaction is 1.36 kJ.

14. Given the equation in question 18, how much heat is involved in the production of 5.0 mol of MgO?

72 kJ

360 kJ

180 kJ

The equation in question refers to the chemical reaction that produces MgO. The question asks for the amount of heat involved in the production of 5.0 mol of MgO. The correct answer of 180 kJ suggests that the reaction releases or absorbs 180 kJ of heat energy when 5.0 mol of MgO is produced. This means that the reaction is exothermic, as it releases heat energy.

Explanation

The equation in question refers to the chemical reaction that produces MgO. The question asks for the amount of heat involved in the production of 5.0 mol of MgO. The correct answer of 180 kJ suggests that the reaction releases or absorbs 180 kJ of heat energy when 5.0 mol of MgO is produced. This means that the reaction is exothermic, as it releases heat energy.

15. Calculate the enthalpy change, H in kJ, for the reaction H2O(s) ---->H2(g) + 1/2O2(g) Use the following: H2(g) + 12O2(g) ---->H2O(l) ^H= 285.9 kJ H2O(s) yH2O(l) H+6.0 kJ

291.9 kJ

+291.9 kJ

279.9 k

The enthalpy change for the reaction is -279.9 kJ. This can be determined by subtracting the enthalpy change for the reaction H2(g) + 1/2O2(g) -> H2O(l) from the enthalpy change for the reaction H2O(s) -> H2O(l). The enthalpy change for the reaction H2(g) + 1/2O2(g) -> H2O(l) is given as 285.9 kJ. Since the reaction in question is the reverse of this reaction, the enthalpy change will have the opposite sign, resulting in -285.9 kJ. Adding this to the enthalpy change for the reaction H2O(s) -> H2O(l) (6.0 kJ), we get a total enthalpy change of -279.9 kJ.

Explanation

The enthalpy change for the reaction is -279.9 kJ. This can be determined by subtracting the enthalpy change for the reaction H2(g) + 1/2O2(g) -> H2O(l) from the enthalpy change for the reaction H2O(s) -> H2O(l). The enthalpy change for the reaction H2(g) + 1/2O2(g) -> H2O(l) is given as 285.9 kJ. Since the reaction in question is the reverse of this reaction, the enthalpy change will have the opposite sign, resulting in -285.9 kJ. Adding this to the enthalpy change for the reaction H2O(s) -> H2O(l) (6.0 kJ), we get a total enthalpy change of -279.9 kJ.