Q: What is the correct formula to calculate the heat required to raise the temperature of a substance?

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

Question 1

Which section of a heating curve represents a change in state, such as melting or boiling?

Accepted Answer

The horizontal lines (plateaus) where temperature remains constant

Question 2

What is the correct formula to calculate the heat required to raise the temperature of a substance?

Accepted Answer

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

Question 3

If 15.0 g of ethanol is heated from 25.0°C to 78.0°C, what is the temperature change ($$\Delta T$$)?

Accepted Answer

$$\Delta T = 53.0$$^{\circ}$$C$$

Question 4

Which of the following best describes what happens during the plateau at the boiling point on a heating curve?

Accepted Answer

The substance undergoes a phase change from liquid to gas

Question 5

Given a specific heat of ethanol of $$2.46 \frac{J}{g$$^{\circ}$$C}$$, how much heat is required to raise the temperature of 15.0 g of ethanol by $$53.0^{\circ}C$?

Accepted Answer

$$1960\ J$$

Question 6

What is the heat of vaporization, and how is it used in calculations involving phase changes?

Accepted Answer

It is the energy required to convert a liquid to a gas at its boiling point; it is multiplied by the mass of the substance.

Question 7

Calculate the total heat required to convert 15.0 g of ethanol at $$25.0^{\circ}C$ to gas at 78.0$$^{\circ}$$C$$ using the following data: specific heat $$2.46 \frac{J}{g$$^{\circ}$$C}$$, heat of vaporization $$841 \frac{J}{g}.$$

Accepted Answer

$$14600\ J$$

Question 8

On a cooling curve for water, what does the plateau at $$100^{\circ}C$ represent?

Accepted Answer

Condensation of steam to liquid water

Question 9

Which equation would you use to calculate the heat required for a phase change from liquid to gas?

Accepted Answer

$$q = m 	imes H_{vap}$$

Question 10

A student claims that during the boiling of water, the temperature continues to rise as heat is added. Is this correct? Why or why not?

Accepted Answer

No, because the temperature remains constant during the phase change.

Question 11

If you have 20.0 g of ethanol at $$25.0^{\circ}C$, how much heat is needed to vaporize it at 78.0$$^{\circ}$$C$$? (Specific heat $$2.46 \frac{J}{g$$^{\circ}$$C}$$, heat of vaporization $$841 \frac{J}{g})$$

Accepted Answer

$$16820\ J$$

Question 12

Which of the following best explains why temperature does not change during a phase change?

Accepted Answer

All the energy is used to break intermolecular forces rather than increase kinetic energy.

Question 13

During which process does water release energy to its surroundings?

Accepted Answer

Condensation

Question 14

A patient receives an ethanol-based medication. If the ethanol must be vaporized in the body, which property is most relevant to calculate the energy required?

Accepted Answer

Heat of vaporization

Question 15

Which of the following is the correct stepwise approach to calculate the total heat required to convert a liquid to a gas starting below its boiling point?

Accepted Answer

Calculate heat to raise temperature to boiling point, then add heat for phase change.

Question 16

If the specific heat of ethanol were doubled, how would this affect the total heat required to raise its temperature from $$25.0^{\circ}C$ to 78.0$$^{\circ}$$C$$?

Accepted Answer

The heat required would double.

Question 17

Which real-world scenario best illustrates the concept of heat of vaporization?

Accepted Answer

Sweat evaporating from skin to cool the body

Question 18

A chemist needs to condense 10.0 g of steam at $$100^{\circ}C$ to liquid water. What equation should be used to calculate the energy released?

Accepted Answer

$$q = m 	imes H_{vap}$$

Question 19

Why is the total heat required to convert a liquid to a gas at its boiling point greater than the heat required to simply raise its temperature to the boiling point?

Accepted Answer

Because breaking intermolecular forces during vaporization requires much more energy than increasing kinetic energy

Heating and Cooling Curves & Combined Heat Calculations

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