Q: Which of the following best describes the order of magnitude of the number 75,000?

It is 4, because $$75,000 = 7.5 \times 10^4$

Q: A student is asked to convert 2.5 kilometers to meters using SI prefixes. Which of the following is the correct conversion?

$$2.5 \ \text{km} = 2.5 \times 10^3$ \ \text{m}$$

Q: Which of the following is a correct expression for the amount of heat required to raise the temperature of 50.0 g of water by 10.0°C, given the specific heat capacity of water is $$4.18 \ \text{J/g} \cdot \text{K}$$?

$$q = 4.18 \times 50.0 \times 10.0$$

Q: The reaction $$\mathrm{S_8$(s) + 8O_2(g) \rightarrow 8SO_2(g)}$$ evolves $$9.31 \ \text{kJ}$$ per gram of sulfur. If the molar mass of $$\mathrm{S_8$} is$$ $$256.56 \ \text{g/mol}$$, what is the enthalpy change per mole of $$\mathrm{S_8$}$$?

$$\Delta H = -2.39 \times 10^3$ \ \text{kJ}$$

Q: Which of the following best describes the relationship between the heat lost by a system and the heat gained by the surroundings in a perfectly insulated calorimeter?

$$q_{\text{system}} + q_{\text{surroundings}} = 0$$

Q: If 1 calorie is defined as the amount of energy required to raise the temperature of 1 gram of water by 1°C, how many joules is 1 calorie equivalent to?

$$1 \ \text{cal} = 4.184 \ \text{J}$$

Question 1

Which of the following best describes the order of magnitude of the number 75,000?

Accepted Answer

It is 4, because $$75,000 = 7.5 	imes 10^4$

Question 2

A student is asked to convert 2.5 kilometers to meters using SI prefixes. Which of the following is the correct conversion?

Accepted Answer

$$2.5 \ 	ext{km} = 2.5 	imes 10^3$ \ 	ext{m}$$

Question 3

Why is it important to use the correct number of significant figures when reporting the result of a calculation in thermochemistry?

Accepted Answer

Because significant figures reflect the precision of the measurements and prevent overstating the certainty of results.

Question 4

A calorimeter is used to measure the heat of a reaction. In an isobaric calorimeter (constant pressure), which of the following equations correctly relates the heat measured to the enthalpy change?

Accepted Answer

$$q = \Delta H$$

Question 5

A reaction in a bomb calorimeter (constant volume) releases 5000 J of heat. What is the value of $$\Delta U$$ for the reaction?

Accepted Answer

$$\Delta U = 5000 \ 	ext{J}$$

Question 6

Which of the following is a correct expression for the amount of heat required to raise the temperature of 50.0 g of water by 10.0°C, given the specific heat capacity of water is $$4.18 \ 	ext{J/g} \cdot 	ext{K}$$?

Accepted Answer

$$q = 4.18 	imes 50.0 	imes 10.0$$

Question 7

A student measures the length of a table as 1.234 m using a ruler marked in millimeters. Which statement best describes the number of significant figures in this measurement?

Accepted Answer

It has 4 significant figures.

Question 8

Which of the following is NOT a source of uncertainty in thermodynamic measurements?

Accepted Answer

Errors caused by using the correct SI units.

Question 9

The reaction $$\mathrm{S_8$(s) + 8O_2(g) ightarrow 8SO_2(g)}$$ evolves $$9.31 \ 	ext{kJ}$$ per gram of sulfur. If the molar mass of $$\mathrm{S_8$} is$$ $$256.56 \ 	ext{g/mol}$$, what is the enthalpy change per mole of $$\mathrm{S_8$}$$?

Accepted Answer

$$\Delta H = -2.39 	imes 10^3$ \ 	ext{kJ}$$

Question 10

A NASA spacecraft was lost due to a unit conversion error. What was the main cause of this error?

Accepted Answer

One team used Imperial units while another used Metric units.

Question 11

Which of the following best describes the relationship between the heat lost by a system and the heat gained by the surroundings in a perfectly insulated calorimeter?

Accepted Answer

$$q_{	ext{system}} + q_{	ext{surroundings}} = 0$$

Question 12

If 1 calorie is defined as the amount of energy required to raise the temperature of 1 gram of water by 1°C, how many joules is 1 calorie equivalent to?

Accepted Answer

$$1 \ 	ext{cal} = 4.184 \ 	ext{J}$$

Question 13

Which of the following equations is used to calculate the heat required to change the temperature of a sample using its heat capacity?

Accepted Answer

$$q = C \Delta T$$

Question 14

A chemical reaction is performed in a bomb calorimeter and the temperature of the water increases. Which of the following statements is correct?

Accepted Answer

The reaction released heat, which was absorbed by the water.

Question 15

Which of the following is the correct sequence of unit conversions when using stoichiometry to calculate the heat produced from a given mass of reactant?

Accepted Answer

Grams $$\rightarrow$$ moles $$\rightarrow$$ kilojoules

Question 16

A student estimates the yearly gasoline consumption in Canada using the following data: 20 million cars, each driving 20,000 km/year, with a consumption of 10 L/100 km. What is the estimated total yearly gasoline consumption?

Accepted Answer

$$4 	imes 10$$^{10}$$ \ 	ext{L}$$

Question 17

Which of the following best explains why calculations cannot increase the accuracy of a measurement?

Accepted Answer

Because the accuracy is limited by the least precise measurement used.

Question 18

Which of the following is a correct statement about the difference between specific heat capacity and molar heat capacity?

Accepted Answer

Specific heat capacity is the heat required to raise the temperature of one gram of a substance by one degree Celsius, while molar heat capacity is for one mole.

Thermochemistry, Calorimetry, and Scientific Measurement in Chemistry

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