How do we calculate the heat required to change the temperature, to melt or evaporate the body?

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Jak obliczamy ciepło potrzebne do zmiany temperatury, stopienia lub wyparowania ciała?

You will learn

to describe in English processes in which the body takes or emits energy in the process of heating, cooling, meltingmeltingmelting, solidification, evaporationevaporationevaporation and condensation,
the definitions of specific heatspecific heatspecific heat, meltingmeltingmelting (solidification) and evaporationevaporationevaporation (condensation) heat as well as to calculate the amount of energy required to heat the body to increase its temperature, to melt or evaporate a certain amount of substance.

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nagranie abstraktu

Please answer the following questions.

What is the specific heatspecific heatspecific heat and what is its unit?
Specify the formula with which you can determine the heat required to heat the substance with mass m by Δt.
What is the heat of meltingmeltingmelting of substances and what is its unit?
Present the method for determining the heat required to melt the body with mass m at the meltingmeltingmelting point.
What is the heat of evaporationevaporationevaporation of substances and what is its unit?
Present the method for determining the heat required to evaporate liquids with mass m.

Answer the following questions and compare your answers with the model answers.

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nagranie abstraktu

1. What is the specific heat and what is its unit?

Specific heatspecific heatSpecific heat - the amount of thermal energy required to increase the heat one kilogram of substance by one degree Celsius (one Kelvin). It is the quantity which characterizes a given substance. In the SI system the unit of specific heatspecific heatspecific heat is $[\frac{J}{k g \cdot K}]$ .

This definition can be written using the following formula:

c_{w} = \frac{Q}{m \cdot ∆ t}

where:
$c_{w}$ - is the specific heatspecific heatspecific heat of the substance,
Q - the heat that must be added to heat the body,
m - the mass of heated body,
Δt - the change in temperature of the body.

Table 1
Solids	Specific heatspecific heatSpecific heat $[\frac{J}{k g \cdot K}]$	Liquids	Specific heatspecific heatSpecific heat $[\frac{J}{k g \cdot K}]$	Gases	Specific heatspecific heatSpecific heat $[\frac{J}{k g \cdot K}]$
lead	130	mercury	140	methane	1854
glass	700	paraffin	2210	carbon dioxide	654
cooper	380	petrol	2090	air	729
gold	130	glycerin	2430	helium	3140
ice	2090	water	4180	water vapor	1380
concrete	920	ether	2340	oxygen	649

Table 1 shows the selected specific heatspecific heatspecific heat of solids, liquids and gases.

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nagranie abstraktu

2. Specify the formula with which you can determine the heat required to heat the substance with mass m by Δt.

By converting the definitional formula of specific heatspecific heatspecific heat, we get the formula for the heat required to heat the body with mass m to obtain the temperature change of Δt:

Q = m \cdot c_{w} \cdot ∆ t

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nagranie abstraktu

3. What is the heat of melting of substances and what is its unit?

Heat of meltingmeltingmelting - the amount of heat (energy) which should be added to 1 kilogram of substance to melt it. This is the quantity which characterizes a given substance. In SI system the unit of melting heatmelting heatmelting heat is $[\frac{J}{k g}]$ . This definition can be written using the following formula:

L równa się Q podzielić przez m.

where:
L - the melting heatmelting heatmelting heat of a substance,
Q - the amount of heat added to a substance during the meltingmeltingmelting process,
m - the mass of the melted body.

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nagranie abstraktu

4. Present the method for determining the heat required to melt the body with mass m at the melting point.

By converting the definition formula of the melting heatmelting heatmelting heat we get:

Q równa się m pomnożyć przez L.

Table 2
Solids	Melting heatmelting heatMelting heat $[\frac{J}{k g}]$
lead	25000
zinc	118000
gold	63000
iron	270000
ice	335000

Table 2 shows selected values of melting heatmelting heatmelting heat for solids.

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nagranie abstraktu

5. What is the heat of evaporation of substances and what is its unit?

Evaporation heatevaporation heatEvaporation heat - the amount of heat (energy) which should be added to 1 kilogram of substance to make it evaporate. This is the quantity which characterizes a given substance. In SI system the unit of melting heatmelting heatmelting heat is $[\frac{J}{k g}]$ . This definition can be written using the following formula:

R = \frac{Q}{m}

where:
R - the evaporation heatevaporation heatevaporation heat of a substance,
Q - the amount of heat added to the substance during the evaporationevaporationevaporation process,
m - the mass of the evaporated body.

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nagranie abstraktu

6. Present the method for determining the heat required to evaporate liquids with mass m.

By converting the definition formula of the evaporation heatevaporation heatevaporation heat we get:

Q = m \cdot R

Table 3
LiquidliquidLiquid	Evaporation heatevaporation heatEvaporation heat $[\frac{J}{k g}]$
mercury	290000
ether	355000
acetic acid	395000
ethanol	963000
water	2260000

Table 3 shows selected values of evaporation heat for liquids.

Summary

The amount of heat energy Q for heating the body depends on the temperature change we want to observe, as well as on the mass of the heated body and the type of substance.
Specific heatspecific heatSpecific heat is used to compare the thermal properties of bodies.
Specific heatspecific heatSpecific heat - the amount of thermal energy required to heat one kilogram of substance to be raised by one degree Celsius (one Kelvin). Specific heat is the quantity that characterizes a given substance.
In order to melt a solidsolidsolid, energy must be added, and in order to solidify the liquidliquidliquid (to change its state from the liquid to solid), energy must be taken away from it.
Melting heatmelting heatMelting heat is the amount of heat (energy) which should be added to 1 kilogram of substance to melt it. This is the quantity which characterizes a given substance.
Freezing heat is the amount of energy that should be taken away to solidify 1 kilogram of a substance.
EvaporationevaporationEvaporation of liquids and boiling (evaporationevaporationevaporation in the whole volume of liquidliquidliquid) requires a supply of heat energy to the liquidliquidliquid, whereas condensation requires energy abstraction from the substance in the gas phase.
Evaporation heatevaporation heatEvaporation heat - the amount of heat (energy) which should be added to 1 kilogram of substance to make it evaporate (to change its state from the liquid to gas). This is the quantity which characterizes a given substance.
Condensation heat - the amount of heat (energy) which should be abstracted to condense 1 kilogram of a substance. This is the quantity which characterizes a given substance.

Exercises

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Exercise 1

Determine which sentences are true.

The specific heat of solids is always greater than the specific heat of the liquid.
The melting heat is characteristic for a given substance and depends on the state of matter.
The heat of evaporation has a higher value than the heat of melting for the same substance.
Water under normal pressure evaporates only at 100°C.
Only in the process of boiling the liquid evaporates on the entire surface.

zadanie

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Exercise 2

Wersja alternatywna ćwiczenia: Note: the required data for calculations are presented in Table 1, Table 2 and Table 3. Determine which sentences are true. Możliwe odpowiedzi: 1. The specific heat of water is very large and it is equal to 4180

\frac{J}{k g \cdot K}

., 2. So to heat water with the mass of 200 g from the initial temperature 20°C to the boiling point, we need to add at least 66880 J of heat., 3. If we provide this heat at the rate of 800

\frac{J}{s}

, the time required to boil the water will be 83,6 s. The mass of the water is 200 g, the initial temperature is 20°C., 4. On the other hand, evaporating 200 g of water would take 452 seconds, if the heat was delivered to the water at the rate of 100 W., 5. If it we want to change 5 kg of ice at 10°C into steam at 100°C, the process would require the energy of at least 33925,5 kJ.

Note: the required data for calculations are presented in Table 1, Table 2 and Table 3. Determine which sentences are true.

The specific heat of water is very large and it is equal to 4180 $\frac{J}{k g}$ .
So to heat water with the mass of 200 g from the initial temperature 20°C to the boiling point, we need to add at least 66880 J of heat.
If we provide this heat at the rate of 800 $\frac{J}{s}$ , the time required to boil the water will be 83,6 s. The mass of the water is 200 g, the initial temperature is 20°C.
On the other hand, evaporating 200 g of water would take 452 seconds, if the heat was delivered to the water at the rate of 100 W.
If it we want to change 5 kg of ice at 10°C into steam at 100°C, the process would require the energy of at least 33925,5 kJ.

Exercise 3

You have a kettle with very good thermal insulationthermal insulationthermal insulation, e.g. porcelain. Design an experiment that would allow to:

a) compare the heat of different liquids,

b) check if the specific heat of water depends on the water temperature.

Write a short instruction in English and design a measurement table. Ask your teacher to help.

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Exercise 4

Indicate which pairs of expressions or words are translated correctly.

ciepło właściwe - specific heat
parowanie - evaporation
topnienie - melting
ciepło parowania - evaporation heat
ciepło topnienia - kind of substance
rodzaj substancji - melting heat

zadanie

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Match Polish terms with their English equivalents.

melting heat
parowanie
evaporation heat
evaporation
melting
ciepło parowania
ciepło topnienia
ciepło właściwe
topnienie
specific heat

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Glossary

evaporation

parowanie

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wymowa w języku angielskim: evaporation

evaporation heat

ciepło parowania

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wymowa w języku angielskim: evaporation heat

liquid

ciecz

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wymowa w języku angielskim: liquid

melting

topnienie

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wymowa w języku angielskim: melting

melting heat

ciepło topnienia

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wymowa w języku angielskim: melting heat

solid

ciało stałe

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wymowa w języku angielskim: solid

specific heat

ciepło właściwe

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wymowa w języku angielskim: specific heat

thermal insulation

izolacja termiczna

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wymowa w języku angielskim: thermal insulation

Keywords

specific heatspecific heatspecific heat

evaporationevaporationevaporation

meltingmeltingmelting

evaporation heatevaporation heatevaporation heat

melting heatmelting heatmelting heat

Scenariusz

1. What is the specific heat and what is its unit?

2. Specify the formula with which you can determine the heat required to heat the substance with mass m by Δt.

3. What is the heat of melting of substances and what is its unit?

4. Present the method for determining the heat required to melt the body with mass m at the melting point.

5. What is the heat of evaporation of substances and what is its unit?

6. Present the method for determining the heat required to evaporate liquids with mass m.

Summary

Exercises

Glossary

Keywords