Heat Energy Flashcards
1
Q
What are the two methods to determine the specific heat capacity of a liquid discussed in the text?
A
The method of mixtures and the electrical method.
2
Q
In the method of mixtures for determining the specific heat capacity of a liquid
A
what is heated instead of the liquid?
3
Q
What is the formula used in the method of mixtures to determine the specific heat capacity of a liquid?
A
Heat gained by water + heat gained by calorimeter = Heat lost by solid.
4
Q
Give the full expansion of the formula “Heat gained by water + heat gained by calorimeter = Heat lost by solid”.
A
m₁ c₁ (θ₂ - θ₁) + m₂ c₂ (θ₂ - θ₁) = m₃ c₃ (θ₃ - θ₂)
5
Q
Define the terms in the full expansion of the heat exchange formula.
A
m₁ = mass of water
6
Q
What is the main difference between determining the specific heat capacity of a solid and a liquid using the method of mixtures?
A
The liquid is not heated directly; instead
7
Q
What is the first step in the experiment to determine the specific heat capacity of a solid?
A
Weigh the solid using a chemical balance and record the mass (m₃).
8
Q
What is done after weighing the solid?
A
Heat it by suspending it in boiling water in a container until it attains the temperature of the boiling water.
9
Q
While the solid is being heated
A
what is done with the calorimeter?
10
Q
What liquid is poured into the calorimeter to about half its volume?
A
Water.
11
Q
What is done after pouring water into the calorimeter?
A
It is reweighed to determine the mass of the water (m₁).
12
Q
What is recorded before transferring the hot solid into the calorimeter?
A
The initial temperature (θ₁) of the water in the calorimeter.
13
Q
How is the hot solid transferred into the calorimeter?
A
Quickly
14
Q
What is done after transferring the solid into the calorimeter?
A
The mixture is stirred gently
15
Q
What is the material of the calorimeter?
A
Usually copper.
16
Q
What is the formula used to calculate the specific heat capacity of the solid (c₃)?
A
m₁ c₁ (θ₂ - θ₁) + m₂ c₂ (θ₂ - θ₁) = m₃ c₃ (θ₃ - θ₂)
17
Q
What is the principle of the method of mixtures?
A
Heat lost by hot bodies = Heat gained by cold bodies + Heat gained by the container.
18
Q
What assumptions are made in applying the method of mixtures?
A
That there is no heat lost to the surroundings.
19
Q
Is the assumption that no heat is lost to the surroundings ever strictly correct?
A
No.
20
Q
What is a calorimeter?
A
A specially designed container used in heat experiments to minimize heat loss to the surroundings.
21
Q
Give the formula for the quantity of heat (ΔQ) supplied to a substance.
A
ΔQ = m c ΔT
22
Q
Define the terms in the formula for heat supplied.
A
ΔQ = the quantity of heat supplied
23
Q
What is specific heat capacity (c)?
A
The quantity of heat required to raise the temperature of 1 kg mass of the substance through 1 K or 1°C.
24
Q
What is the formula for specific heat capacity (c)?
A
c = ΔQ / (m ΔT)
25
Define the terms in the specific heat capacity formula.
ΔQ = the quantity of heat supplied
26
What is the unit of specific heat capacity?
J kg⁻¹ K⁻¹ or J kg⁻¹ °C⁻¹ (joules per kilogram per kelvin or joules per kilogram per degree Celsius).
27
How does specific heat capacity vary between substances?
It differs from one substance to another.
28
Does the specific heat capacity of a substance change with its state?
Yes.
29
What is heat capacity (C)?
The amount of heat required to raise its temperature by 1 K or 1°C.
30
What is the formula for heat capacity (C)?
C = ΔQ / ΔT
31
Define the terms in the heat capacity formula.
ΔQ = the quantity of heat supplied
32
What is the unit of heat capacity?
J/K or J/°C (joules per kelvin or joules per degree Celsius).
33
Does the heat capacity vary from object to object?
Yes.
34
On what factors does the heat capacity of a substance depend?
The nature and mass of the substance.
35
Does a given object always have the same heat capacity?
No
36
Do most liquids expand when heated and contract when cooled?
Yes.
37
Is water an exception to the general rule of liquid expansion?
Yes.
38
How does water behave when cooled?
It contracts on cooling from any temperature until 4°C
39
At what temperature does water have its least volume and highest density?
4°C.
40
What is a significant consequence of water's anomalous expansion?
Ponds
41
Why is the anomalous expansion of water important for marine life?
It allows marine life to survive during winter because the bottom of the lake remains at a temperature warm enough for aquatic life (4°C).
42
What experiment is used to illustrate the anomalous behavior of water?
Hope's experiment.
43
What does Hope's apparatus consist of?
A metal cylinder filled with water and surrounded by a circular tray containing a freezing mixture of ice and salt.
44
What do thermometers A and B measure in Hope's experiment?
Thermometer A measures the water temperature near the surface
45
What is the initial temperature reading of thermometers A and B in Hope's experiment?
The same.
46
What happens to the temperature readings shortly after the experiment begins?
Thermometer B shows a rapid fall
47
What happens when the reading of thermometer B falls to 4°C?
It remains constant
48
What happens when thermometer A reaches 0°C?
The water at the surface of the cylinder changes into ice.
49
Explain why the water at the bottom of Hope's apparatus cools to 4°C first.
The water in the middle cools
50
What is the relationship between mass (M)
volume (V)
51
How does density vary with volume?
Density decreases as volume increases.
52
How does volume vary with temperature?
Volume increases with temperature.
53
How does density vary with temperature?
Density decreases with temperature (since mass is constant).
54
Give the formula relating initial volume (V₁) and final volume (V₂) with cubic expansivity (γ) and temperature change (θ).
V₂ = V₁ (1 + γθ)
55
Give the formula relating density at a lower temperature (d₁) and density at a higher temperature (d₂) with cubic expansivity (γ) and temperature change (θ).
d₁ = d₂ (1 + γθ)
56
What is the first step in the experiment to determine the apparent cubic expansivity of a liquid?
Clean and dry a relative density bottle and weigh it.
57
What is done after cleaning and drying the bottle?
It is filled with the liquid whose apparent cubic expansivity is required.
58
After filling the bottle
what is done next?
59
Where is the bottle then suspended?
From the clamp of a retort stand
60
What is recorded at this stage?
The temperature of the water.
61
How is the water in the beaker heated?
Gently with a Bunsen burner until it boils.
62
What happens as the water is heated?
Some liquid is expelled through the orifice of the bottle stopper.
63
When is the heating stopped?
When no more liquid is expelled from the relative density bottle.
64
What is recorded at the end of the heating process?
The temperature of the boiling water.
65
What is done after heating?
The bottle is removed
66
How is the apparent cubic expansivity of the liquid calculated?
Using the formula: γₐ = (M₂ - M₃) / ((M₃ - M₁) x (θ₂ - θ₁)).
67
Define the terms in the formula for apparent cubic expansivity.
M₁ = mass of empty bottle
68
Why is it necessary to distinguish between real and apparent cubic expansivity of a liquid?
Because the expansion of liquids is complicated by the expansion of their containers.
69
Define real expansion of a liquid.
Apparent expansion + expansion of the container.
70
Define real (or absolute) cubic expansivity (γᵣ) of a liquid.
The increase in volume per unit volume per degree rise in temperature.
71
Define apparent cubic expansivity (γₐ) of a liquid.
The increase in volume per unit volume per degree rise in temperature when the liquid is heated in an expansible vessel.
72
Is the real expansivity of a liquid more or less than its apparent expansivity?
More than.
73
What is the relationship between the real and apparent expansivity of a liquid and the cubic expansivity of the vessel?
γᵣ = γₐ + γ (where γ is the cubic expansivity of the vessel).
74
Do liquids expand or contract when heated?
Expand.
75
Do liquids expand or contract when cooled?
Contract.
76
Why is the expansion of liquids often complicated?
Because liquids are usually held in a container
77
Describe the experiment to demonstrate liquid expansion.
Fill a flask with colored water
78
What is observed in the liquid expansion experiment?
The liquid level initially falls slightly and then rises steadily as more heat is applied.
79
Why does the liquid level initially fall in the experiment?
Because the glass flask expands before the liquid.
80
What happens to the liquid level as more heat is applied?
The expansion of the liquid becomes greater than that of the glass
81
What happens to the liquid level when heat is removed?
The liquid contracts
82
Do equal volumes of different liquids expand by the same amount when heated through the same temperature range?
No.
83
What happens to a thick glass tumbler when hot water is poured into it?
It cracks.
84
Why does a thick glass tumbler crack when hot water is poured into it?
The inside of the tumbler expands more rapidly than the outside
85
What type of glass is used for laboratory beakers and flasks to avoid cracking?
Pyrex.
86
Why is pyrex glass used for laboratory glassware?
It has a low thermal expansivity.
87
How can a tight glass stopper be removed from a glass bottle without cracking it?
By standing the bottle in hot water (making sure the stopper is not in the water) or by warming the neck of the bottle with a flame.
88
Why does warming the bottle's neck help in removing a tight stopper?
As the bottle expands
89
Give examples of useful applications of expansivity.
Fixing metal tyres onto metal wheels in locomotives
90
Why is the force of contraction when a hot metal cools utilized in riveting?
To rivet together steel plates and girders in shipbuilding
91
Why are platinum wires used when wires are to be fused through glass vessels?
Because platinum and glass have approximately the same expansivity.
92
What is a bimetallic strip?
A strip of two different metals
93
Why does a bimetallic strip bend when heated?
Because the two metals have different expansivities and expand by different amounts.
94
Which metal is on the outside of the curve when a bimetallic strip is heated?
The metal with the greater linear expansivity.
95
What are some applications of bimetallic strips?
Balance wheels of clocks and watches
96
How does a bimetallic strip compensate for temperature changes in clocks and watches?
It bends inward on expansion
97
What metals are typically used in a bimetallic strip thermometer?
Invar (which hardly expands) and brass.
98
How does a bimetallic strip thermometer work?
Uneven expansion of the metals causes the strip to curve
99
How is a bimetallic strip used in an electric thermostat?
To control the temperature of an appliance like an electric laundry iron.
100
Describe how a bimetallic strip regulates temperature in an electric iron.
The strip bends away from a contact point to switch off the current when the desired temperature is reached
101
How does a bimetallic strip function in a fire alarm?
Heat from a fire causes the strip to bend and complete a circuit
102
What are some consequences and applications of expansion discussed in the text?
Expansion in buildings and steel bridges
103
What causes creaking noises in the roofs of buildings?
The expansion of the metal sheets as they get heated by the sun.
104
What happens to steel girder bridges during the day?
They expand when heated.
105
What is used to allow for the expansion of steel bridges?
Expansion gaps with rollers.
106
Why are gaps left between rails in railway lines?
To allow for free expansion and contraction of the rails.
107
What can happen to railway lines on hot days if there are no gaps?
They can buckle
108
What happens to telegraph wires during the hot season?
They expand and sag.
109
Why are telegraph wires given a certain amount of sag?
So they can contract in cold weather without snapping.
110
If a sheet of metal has an initial length l₁ and breadth b₁
what is the initial area (A₁) of the sheet?
111
If the length and breadth of the metal sheet are l₂ and b₂ after heating
what is the final area (A₂) of the sheet?
112
Give the formula for l₂ in terms of l₁ and linear expansivity (α).
l₂ = l₁ (1 + αθ)
113
Give the formula for b₂ in terms of b₁ and linear expansivity (α).
b₂ = b₁ (1 + αθ)
114
Give the formula for A₂ in terms of l₁
b₁
115
Why can α² be neglected in the equation A₂ = l₁b₁ (1 + 2αθ + α²θ²)?
Because α is a very small quantity
116
Using the approximation
give the simplified formula for A₂.
117
From a previous formula
A₂ = A₁ (1 + βθ). Comparing this with A₂ = l₁b₁ (1 + 2αθ)
118
What is the relationship between cubic or volume expansivity (γ) and linear expansivity (α)?
γ = 3α
119
In what directions does a solid expand when heated?
In all directions - length
120
What increases as a result of a solid being heated?
Area and volume.
121
What is the increase in area when a body is heated called?
Area or superficial expansion.
122
Define area or superficial expansivity (β).
The increase in area per unit area per degree Kelvin increase in temperature or the fractional increase in area per Kelvin rise in temperature.
123
Define volume or cubic expansivity (γ).
The increase in volume of a substance per unit volume per Kelvin rise in temperature or the fractional increase in volume per Kelvin rise in temperature.
124
Give the formula for area expansivity (β).
β = (A₂ - A₁) / (A₁ x θ)
125
Define the terms in the area expansivity formula.
A₂ = area at temperature θ₂
126
Give the formula for A₂ (area at temperature θ₂).
A₂ = A₁ (1 + βθ)
127
Give the formula for the increase in area.
A₂ - A₁ = A₁ βθ
128
Give the formula for cubic expansivity (γ).
γ = (V₂ - V₁) / (V₁ θ)
129
Define the terms in the cubic expansivity formula.
V₂ = volume at temperature θ₂
130
Give the formula for V₂ (volume at temperature θ₂).
V₂ = V₁ (1 + γθ)
131
Give the formula for the increase in volume.
V₂ - V₁ = V₁ γθ
132
What is the first step in the experiment to determine the linear expansivity of a metal rod?
Measure the length of the metal rod with a metre rule.
133
Where is the rod inserted after measuring its length?
Into the steam jacket.
134
How is one end of the metal rod (A) fixed?
Firmly.
135
What is done with the other end of the rod (B)?
It lies just outside the steam jacket and is free to move.
136
What is initially run through the jacket?
Cold water.
137
What is read to determine the initial temperature of the cold rod?
The thermometer.
138
What instrument is used to touch the free end of the rod
and what is recorded?
139
After taking the initial reading of the screw gauge
what is done with it?
140
What is passed through the steam jacket to heat the rod?
Steam.
141
What happens to the rod as a result of heating?
It expands.
142
What is done after the rod expands?
The micrometer screw gauge is screwed to make contact with the rod again
143
When is the process repeated?
Until the reading of the screw gauge is constant.
144
What is read to determine the final steady temperature of the rod?
The thermometer inserted into the steam jacket.
145
How is the expansion of the rod calculated?
By finding the difference between the initial and final micrometer readings.
146
Do different solids expand by the same amount when heated over the same temperature range?
No.
147
Give an example of two solids that expand by different amounts.
Copper expands more than steel when both are heated through the same rise in temperature.
148
What is linear expansivity (α)?
The increase in length per unit length per degree rise in temperature.
149
Give the formula for linear expansivity (α).
α = (l₂ - l₁) / (l₁ (θ₂ - θ₁)) = e / (l₁ θ)
150
Define the terms in the linear expansivity formula.
α = linear expansivity
151
What is the unit of linear expansivity (α)?
per °C or per K (K⁻¹)
152
What does it mean if the linear expansivity of copper is 0.000017 K⁻¹?
A unit length of copper expands by 0.000017 units when it is heated through 1 K (or 1 °C) rise in temperature.
153
Give the formula for the new length (l₂) of a metal after heating.
l₂ = l₁ (1 + αθ)
154
How does the value of linear expansivity (α) vary between substances?
It differs from substance to substance.
155
For what type of materials is linear expansivity highest?
Metals.
156
What happens to solids when heated?
They expand.
157
What happens to solids when cooled?
They contract.
158
What experiment demonstrates the expansion and contraction of solids?
The 'ball and ring experiment'.
159
Describe the ball and ring experiment.
A metal ring through which a metal ball just fits at room temperature. When the ball is heated
160
What does the ball and ring experiment show?
That the metal ball increases in size when heated and decreases in size when cooled.
161
What is another experiment that demonstrates the expansion and contraction of solids?
The 'bar and gauge experiment'.
162
Describe the bar and gauge experiment.
A bar that just fits into the gauge at ordinary room temperature. When the bar is heated
163
What happens to most solids and liquids when heated?
They expand.
164
What happens to most solids and liquids when cooled?
They contract.
165
What does expansion mean?
An increase in the size of an object.
166
According to the kinetic molecular theory
what happens to molecules when an object is heated?
167
What increases as the molecules vibrate more and their displacements about their mean positions increase?
The average distance between the molecules of the substance.
168
What does the increase in the average distance between molecules lead to?
An increase in the size of the substance.
169
On what factor does the increase in the dimension of the heated object depend?
The strength of the intermolecular forces.
170
How does the strength of intermolecular forces affect expansion?
Stronger forces lead to smaller expansion
171
Compare the strength of intermolecular forces in solids
liquids
172
Which expands more when heat is applied: gases
liquids
173
Why do different substances expand differently when heated?
Because each substance has unique intermolecular forces.
174
What kind of energy do molecules possess due to their constant motion?
Kinetic energy.
175
What is temperature a measure of according to the kinetic molecular theory?
The average kinetic energy of its molecules.
176
What happens to the speed of motion of molecules and the average kinetic energy when heat is added to a substance?
It causes an increase.
177
What does an increase in the average kinetic energy of the molecules of a substance result in?
An increase in its temperature.
178
What happens to the motion of the molecules and their average kinetic energy when heat is removed from a body?
It leads to a decrease.
179
What does a reduction in the average kinetic energy of molecules result in?
A decrease in temperature.
180
What is temperature related to
according to the kinetic molecular theory?
181
What does the molecular theory of matter assume?
That matter is made up of atoms that aggregate in molecules.
182
Define an atom.
The smallest particle of an element that can have a separate existence and still retain the chemical properties of that element.
183
Define a molecule.
A group of atoms of the same or different elements joined together in a simple proportion.
184
What is the order of magnitude of the size of a molecule?
10⁻² m.
185
How are molecules arranged in solids?
Fixed in definite positions
186
Why do solids have a fixed shape and volume?
Because the positions of the molecules are fixed due to intermolecular forces of attraction and repulsion.
187
How are molecules arranged in liquids compared to solids?
More free to move about within the liquids.
188
What holds molecules of liquids and solids together?
Intermolecular forces.
189
How are molecules arranged in gases?
In constant motion
190
What does this arrangement allow gases to do?
Take up the shape and volume of their container.
191
How does the distance between gas molecules compare to those in solids and liquids?
Much farther apart.
192
What are the effects of heat on an object?
Change in temperature
193
What does the addition of heat cause regarding temperature (except during a change of state)?
The temperature of a body to rise.
194
What can the addition of heat bring about regarding the state of a body?
A change of state.
195
Give an example of a change of state caused by adding heat to a solid.
Melting from solid (e.g.
196
What may happen when enough heat is added to a liquid?
Vaporization (change from liquid to vapor state) or boiling.
197
What does the addition of heat usually cause regarding the dimensions of a body?
Expansion (increase in size).
198
Name some physical properties of a body that may change with the addition of heat.
Electrical resistance
199
What is thermionic emission?
The emission of electrons from the surface of a metal due to the addition of heat.
200
What changes may occur in the chemical properties of a body when heat is added?
Chemical change.
201
What happens to the pressure and volume of a gas when heat is added?
The pressure and volume increase.
202
What is the temperature of pure melting ice at standard atmospheric pressure?
0°C.
203
What is the temperature of pure boiling water at standard atmospheric pressure?
100°C.
204
What is the temperature range of the Celsius scale?
0°C to 100°C.
205
What is another scale of temperature?
The Kelvin scale.
206
What is the SI unit of temperature?
Kelvin (K).
207
How is the Kelvin scale related to the Celsius scale?
K = °C + 273.
208
What is absolute zero?
The zero of the Kelvin scale (-273°C).
209
Why is absolute zero called absolute zero?
Because it is the lowest temperature attainable.
210
Can a temperature be lower than absolute zero?
No.
211
What is heat?
A form of energy called thermal energy.
212
What happens when we place a pot of cold water on a heating stove?
After a few minutes
213
What do we say happened when a pot of cold water is placed on a heating stove and gets hotter?
Heat flowed from the heating stove to the cold water.
214
What is the common experience with heat flow?
Heat always flows from a hot to a cold object.
215
What happens when a hot object is placed in contact with a cold object?
A hot object always warms the cold one.
216
Does the reverse of heat flow ever occur?
No.
217
What does a cold object never do?
Warm a hot object.
218
Define heat energy.
The energy that is transferred from a hot object to a cooler object as a result of their difference in temperature.
219
Define temperature.
The degree of hotness or coldness of an object.
220
Is temperature a scalar or vector quantity?
Scalar.
221
What is temperature a property of?
An object which decides which way heat will flow when it is placed in contact with another object.
222
In what direction does heat flow?
From a body at a higher temperature to one at a lower temperature.
223
What causes the transfer of heat energy?
The temperature difference between two objects.
224
How does the temperature of a hot body compare to a cold body?
A hot body is at a higher temperature than a cold body.
225
What happens to temperature as a body gets hotter or cooler?
Temperature rises or falls respectively.
226
What instruments are used to measure temperature?
Thermometers.
227
What is the commonest thermometer available in school laboratories?
The Celsius-scale thermometer.
228
What unit is temperature measured in on a Celsius-scale thermometer?
Degree Celsius (°C).
