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XPHD 5th Form Physics MAC > 09 Changes of State and SHC - 4th Form > Flashcards

09 Changes of State and SHC - 4th Form Flashcards

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1
Q

If the specific heat capacity of water is 4200 J/kg°C, how much energy is needed to raise 1 kg of

water by 2°C?

A

8400 J

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2
Q

What is the unit for Energy?

A

Joules

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3
Q

The total energy which matter possesses is called its internal energy.

This is the total kinetic and potential energy of all the particles.

Which state of matter possesses the most energy?

A

gas

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4
Q

Which material has the lowest specific heat capacity? How do you know?

A

aluminium

It requires less energy for the same temperature change as water.

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5
Q

Which state of matter has a fixed volume but an indefinite shape?

A

liquid - it has a fixed volume but can take the shape of its container

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6
Q

Describe the particle movement in a solid

A
  • vibrating in fixed positions
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7
Q

How does the specific heat capacity of water and sand help create a sea breeze shown during the daytime?

A
  • Radiated heat from the Sun is absorbed by sand and water.
  • Sand has a much lower specific heat capacity than water and so the sand heats up more than the water.
  • The hot sand heats the air above it, this hot air expands and becomes less dense and rises
  • Cool air above water moves across to replace it
  • A convection current is set-up
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8
Q

One pan is filled with 500 g of water and the other with 1000g of cooking oil.

Both pans receive the same amount of energy.

If both the water and oil undergo the same temperature change, what does this tell you about the specific heat capacity of cooking oil?

specific heat capacity of water = 4200 J/kg°C

A

specific heat capcity of cooking oil = 2100 J/kg°C

It must be half that of water, as twice the mass of oil requires the same energy to increase in temperature by the same amount.

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9
Q

What is the equation linking energy, mass, specific heat capactiy and change in temperature?

A
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10
Q

If the force of attraction between particles in a liquid is moderate, how does this change when in gaseous form?

A
  • the force of attraction between particles is very weak or negligible, the particles move freely and are far apart in a gas.
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11
Q

What safety precautions must be taken when finding the specific heat capacity of water?

A
  • heater and water will be hot- handle with care, let cool before clearing away
  • water and electricity may lead to an electric shock- do not operate equipment with wet hand, check insulation on wires is intact before using.
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12
Q

Sketch a typical heating curve for a substance.

A
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13
Q

Name the three states of matter

A

solid, liquid and gas

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14
Q

gas to solid

Name the change of state

A

deposition

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15
Q

If ice from a cold freezer is put in a warm room, it absorbs thermal energy.

The ice warms up and begins to melt.

How does the temperature vary with time while the ice warms from -4°C to 4°C?

A
  • as the ice warms up the temperature rises from -4°C to 0°C.
  • at 0°C the temperature of the ice remains constant while the ice melts.
  • when all the ice has melted the temperature begins rise again from 0°C to 4°C
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16
Q

How is kinetic energy of a substance related to its temperature?

A

Kinetic energy is proportional to the average kinetic energy of the particle in the substance

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17
Q

gas to liquid

Name the change of state

A

condensation

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18
Q

Describe the particle movement in a gas

A
  • moving fast and moving freely
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19
Q

How is the energy supplied to the water calculated when finding the specific heat capacity of water?

A

E = IVt

Energy = Current (A) x voltage (V) x time (s)

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20
Q

How do you improve accuracy when measuring the mass of a metal block using a balance?

A
  • tare balance before use
  • place balance on level surface
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21
Q

Which state of matter possesses the most potential energy?

A

gas - particles are the furthest apart

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22
Q

solid to liquid

Name the change of state

A

melting

23
Q

Which state of matter possesses the most kinetic energy?

A

gas - particles are moving the fastest

24
Q

If the specific heat capacity of water is 4200 J/kg°C, how much energy is needed to raise 2 kg of

water by 2°C?

A

4200 x 4 = 16 800 J

25
Q

How do you improve the reliability of your result when measuring the specific heat capacity of a metal block?

A

Repeat the experiment 3 times to see if similar results are obtained

26
Q

What can be done to obtain a more accurate value for the specific heat capacity of a metal?

A
  • lagging, lid and insulating mat- reduces energy loss to surrounding.
  • Turn on heater and allow it to heat up before placing it in the block- reduces energy lost to heating up heater
  • turn off heater and stopwatch but continue to record temperature until peak temperature of block is reached
27
Q

Which state of matter possesses the most kinetic energy?

A

gas - particles are moving the fastest

28
Q

If 1 kilogram of alcohol at 20°C lost 5000 J of energy, what would its final temperature be?

Specific heat capacity of alcohol = 2500J/kg°C

A

change in temperature = E / mc

= 5000J / (1 kg x 2500 J/kg°C)

= 2 °C

20 -2 = 18°C

29
Q

The internal energy of a substance is a measure of two properties. Describe these two properties.

A

Kinetic energy (KE) or movement of particles

Potential energy (PE) or position of particles with respect to each other

internal energy = KE + PE

30
Q

Explain the temperature change in the graph below.

A
  • Q-R the energy supplied increases the kinetic energy of the particles- temperature increases
  • R-S all the energy supplied goes into weakening intermolecular bonds to induce the state change- temperature stays constant
  • S-T - the state change is completed- energy supplied increases the kinetic energy of the particles- raising the temperature once again.
31
Q

If 1 kilogram of alcohol at 20°C absorbed 10 000 J of energy, what would its final temperature be?

Specific heat capacity of alcohol = 2500J/kg°C

A

change in temperature = E / mc

= 10 000J / (1 kg x 2500 J/kg°C)

= 4 °C

20 + 4 = 24°C

32
Q

Which material will cool more quickly?

A

aluminium

less energy needs to be removed for the same temperature drop.

33
Q

What equipment is needed to find the specific heat capacity of an aluminium block?

A
  • aluminium block, power supply, electric heater and thermometer
  • stopwatch
  • voltmeter
  • ammeter
  • lagging for top and side of block
  • mat for bottom of block
34
Q

Describe the particle arrangement in a gas

A
  • far apart - irregular arrangment
35
Q

Describe the particle arrangement in a solid

A
  • close together - regular arrangement
36
Q

Which state of matter has an indefinite volume and indefinite shape?

A

gas - it expand to fill the volume and shape of its container.

37
Q

Samuel used the equipment below to measure the specific heat capacity of water. His value was

5100 J/kg°C.

The true value is 4200J/kg°C.

Explain why his value is too big?

A
  • Not all the energy supplied by the heater goes to the water, some is lost to heating the heater and to the surroundings - Q [energy supplied] is too big

E=IVt

  • as a result the temperature change is too low

A bigger than expected Q divided by a smaller than expected change in T means the specific heat capacity will always be too big!

38
Q

Describe how the temperature varies with time for the cooling curve below

A
  • For the first 4 minutes the temperature drops from 88°C to 80°C at a decreasing rate.
  • From 4 minutes to 11 minutes the temperature remains constant at 80°C
  • At 12 minutes the temperature decreases at an increasing rate.
39
Q

Describe the particle movement in a liquid

A
  • vibrating and slipping past each other
40
Q

When an object is supplied with energy the internal energy of the object increases. This means the kinetic energy of the particles increases and we see -a change in temperature.

A certain points, the energy supplied to a substance is ‘hidden’ and no temperature change is seen. Here the energy which is supplied goes to breaking the intermolecular forces/bonds between the particles.

What is happening at this point?

A

The substance is going through a change of state.

41
Q

Which material has the highest specific heat capacity? How do you know?

A

water

It requires more energy for the same temperature change as aluminium.

42
Q

solid to gas

Name the change of state

A

sublimation

43
Q

Describe the particle arrangement in a liquid

A
  • close together - irregular arrangement
44
Q

liquid to solid

Name the change of state

A

freezing

45
Q

Explain the temperature change with time for the cooling curve below

A
  • As the object is cooled and energy is removed from the substance the internal energy of substance decreases. Kinetic energy of particles decreases- temperature decreases with time
  • At 80°C, the particles form intermolecular forces/bonds as the substance begins to solidify (freeze). This bond formation releases energy to the surroundings and maintains a temperature of 80°C until all the substance freezes.
  • When all the substance is solidified, the energy removed from the substance decreases the kinetic energy of the particles and temperature continues to decrease.
46
Q

liquid to gas

Name the change of state

A

evaporation

47
Q

If 2 kilogram of steel at 20°C absorbed 1000 J of energy, what would its final temperature be?

Specific heat capacity of steel = 500J/kg°C

A

change in temperature = E / mc

= 1000J / (2 kg x 500 J/kg°C)

= 1 °C

20 + 1 = 21°C

48
Q

If the specific heat capacity of water is 4200 J/kg°C, how much energy is needed to raise 2 kg of

water by 1°C?

A

8400 J

49
Q

Define specific heat capacity

A

The energy required to heat 1 kg of a substance by 1°C

50
Q

How does the specific heat capacity of water and sand help create the land breeze during nighttime?

A
  • Both sand and water are cooling
  • Water has a much higher specific heat capacity than sand and so the water cools more slowly than the sand.
  • The hotter water heats the air above it, this hot air expands and becomes less dense and rises
  • Cool air above the sand moves across to replace it
  • A convection current is set-up
51
Q

Calculate the specific heat capacity of the following object

  • mass of block= 1000 g
  • current = 2A
  • voltage = 12 V
  • time = 200 s
  • temperature change = 10°C
A

E = IVt = 2A x V x 200 s = 4800 J

c = 4800 J / (1 kg x 10°C)

c = 480 J/kg°C

52
Q

If the force of attraction between particles in a solid is strong, how does this change when in liquid form?

A
  • the force of attraction between particles is moderate, the particles can now slip past each other
53
Q

Which state of matter has a fixed shape and a fixed volume?

A

solid

54
Q

Most central heating systems use water to carry thermal energy. Why is water a good choice in this application?

A

Water has a very high specific heat capacity.

It is very good a storing energy, carrying it from the boiler and releasing it at the radiators

XPHD 5th Form Physics MAC (20 decks)

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