Q: Which formula is used to calculate the heat absorbed or released by a substance given its mass, specific heat capacity, and temperature change?

$$q = m \times C_s \times \Delta T$$

Question 1

Which of the following statements best describes the law of conservation of energy as it applies to chemical reactions?

Accepted Answer

Energy is transferred between the system and surroundings, but the total energy remains constant.

Question 2

A student drops a ball from a height, and it bounces on the ground. Which energy transformation occurs during this process?

Accepted Answer

Potential energy is converted to kinetic energy.

Question 3

Which equation correctly expresses the relationship between internal energy change, heat, and work for a system?

Accepted Answer

$$\Delta E = q + w$$

Question 4

A 50.0 g sample of metal at 80.0°C is placed in 100.0 g of water at 20.0°C. The final temperature is 25.0°C. If the specific heat capacity of water is $$4.18 \ \mathrm{J/g\cdot ^\circ C}$$, what is the specific heat capacity of the metal? (Assume no heat loss to surroundings.)

Accepted Answer

$$0.42 \ \mathrm{J/g\cdot ^\circ C}$$

Question 5

Which of the following processes is exothermic?

Accepted Answer

Wood burning in a fire

Question 6

What is the sign of $$\Delta H$$ for an endothermic reaction, and what does it indicate?

Accepted Answer

$$\Delta H is $$positive; heat is absorbed from the surroundings.

Question 7

A piston expands from 1.00 L to 2.00 L against an external pressure of 1.00 atm. How much work (in J) is done by the system? ($$1 \ \mathrm{L\cdot atm} = 101.3 \ \mathrm{J})$$

Accepted Answer

$$-101.3 \ \mathrm{J}$$

Question 8

Which of the following is an example of a state function?

Accepted Answer

Internal energy ($$E)$$

Question 9

In a bomb calorimeter, 1.00 g of sucrose ($$C_{12}H$$_{22}$$O_{11}) $$undergoes combustion, raising the temperature of the calorimeter by $$4.09 \ ^\circ C. If $$the heat capacity of the calorimeter is $$4.90 \ \mathrm{J/ ^\circ C}$, what is the heat released by the reaction?

Accepted Answer

$$20.0 \ \mathrm{J}$$

Question 10

Which equation correctly defines enthalpy ($$H) in $$terms of internal energy ($$E$$), pressure ($$P$$), and volume ($$V$$)?

Accepted Answer

$$H = E + PV$$

Question 11

If a chemical equation is reversed, what happens to the sign of $$\Delta H_{rxn}$$?

Accepted Answer

It changes sign.

Question 12

Which of the following best describes the difference between bomb calorimetry and coffee-cup calorimetry?

Accepted Answer

Bomb calorimetry measures $$\Delta E at $$constant volume, while coffee-cup calorimetry measures $$\Delta H at $$constant pressure.

Question 13

Which of the following is true about the standard enthalpy of formation ($$\Delta H_f^\circ) $$for a pure element in its standard state?

Accepted Answer

$$\Delta H_f^\circ is $$zero.

Question 14

A chemical reaction has $$\Delta H_{rxn} = -500 \ \mathrm{kJ}. $$What does this value indicate about the reaction?

Accepted Answer

The reaction is exothermic and releases 500 kJ of heat.

Question 15

Which formula is used to calculate the heat absorbed or released by a substance given its mass, specific heat capacity, and temperature change?

Accepted Answer

$$q = m 	imes C_s 	imes \Delta T$$

Question 16

Which of the following statements about breaking and forming chemical bonds is correct?

Accepted Answer

Breaking bonds always absorbs energy.

Question 17

If the enthalpy change for a reaction is $$\Delta H_{rxn} = +250 \ \mathrm{kJ}$$, which of the following processes could this represent?

Accepted Answer

Sweat evaporating from skin

Question 18

Using Hess's Law, which of the following is true?

Accepted Answer

The enthalpy change for an overall reaction is the sum of the enthalpy changes for each step.

Question 19

A chemical hand warmer contains iron powder that reacts with oxygen to form iron oxide and heat. Which type of energy is primarily released in this process?

Accepted Answer

Thermal energy

Chapter 7: Thermochemistry – Study Notes

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