N5 Heat & Properties of Matter Flashcards

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1
Q

What does the particle model (or kinetic theory) tell us about the particles of a an ideal gas?

A

The particles of an ideal gas are in constant random motion.

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2
Q

Define temperature.

A

The temperature of a substance is a measure of the mean kinetic energy of its particles

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3
Q

What happens to the temperature of a substance when it
a) gains heat energy
b) loses heat energy

A

The temperature of a substance:

a) increases when heat it gains heat energy.

.b) decreases when heat loses. heat energy/

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4
Q

Define the specific heat capacity (c) of a substance.

A

The specific heat capacity (c) of a substance is the amount of heat energy required to raise the temperature of 1 kg of the substance by 1 °C.

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5
Q

Eh = cmΔT

(Define symbols and units)

A

Eh - Heat energy (J)

c - specific heat capacity (J kg-1 °C-1 - see data sheet)

m - mass (kg)

ΔT - Change in temperature (°C)

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6
Q

Calculate the amount of heat energy required raise the temperature of 2 kg of water in a kettle from room temperature (20 °C) to boiling point (100°C).

A
E<sub>h</sub> = ?
c = 4180 J kg<sup>-1</sup> °C<sup>-1</sup> (from data sheet)
m = 2 kg
ΔT = 100 - 20 = 80 °C
*E<sub>h</sub> = cmΔT
E<sub>h</sub> = 4180 x 2 x 80
E<sub>h</sub> = 669 000 J (to 3sf)*
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7
Q

What happens to a substance when heat is gained or lost at its melting or boiling point?

A

The substance will change state.

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8
Q

Describe what happens to the particles of a substance when it changes state.

A

The bonds between particles are either loosened or strengthened (meaning the particles gain or lose potential energy).

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9
Q

What happens to the temperature of a substance during a change of state?

A

There is no change in temperature during a change of state.

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10
Q

Eh = ml

(Define symbols and units)

A

Eh - Heat energy (J)

m - mass (kg)

l - specific latent heat (J kg-1 - see data sheet)

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11
Q

Example

How much water will evaporate when 500 kJ of heat is applied?

A

Eh = 500 kJ = 500 x 103 J
m - ?
l = 22·6 x 105 J kg-1 (from data sheet)

Eh = ml
500 x 103 = m x 22·6 x 105
m x 22·6 x 105 = 500 x 103
m = 500 x 103/22·6 x 105
m = 0·221 kg

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12
Q

The heating curve (graph of temperature versus time) for a substance is shown.

What is happening in the section labelled A?

A

(The substance is a solid to begin with because there are only three states of matter with solid being the coolest).

The substance is increasing temperature as a solid.

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13
Q

The heating curve (graph of temperature versus time) for a substance is shown.

What is happening in the section labelled B?

A

(The substance is a solid to begin with because there are only three states of matter with solid being the coolest).

The substance is changing state from solid to liquid.

(i.e. the substance is melting)

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14
Q

The heating curve (graph of temperature versus time) for a substance is shown.

What is happening in the section labelled C?

A

(The substance is a solid to begin with because there are only three states of matter with solid being the coolest).

The substance is increasing in tempearture as a liquid.

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15
Q

The heating curve (graph of temperature versus time) for a substance is shown.

What is happening in the section labelled D?

A

(The substance is a solid to begin with because there are only three states of matter with solid being the coolest).

The substance is changing state from liquid to gas.

(i.e. the substance is vaporising (boiling).).

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16
Q

The heating curve (graph of temperature versus time) for a substance is shown.

What is happening in the section labelled E?

A

(The substance is a solid to begin with because there are only three states of matter with solid being the coolest).

The substance is increasing in temperature as a gas.

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17
Q

The heating curve (graph of temperature versus time) for a substance is shown.

What is the melting point of the substance?

A

(The substance is a solid to begin with because there are only three states of matter with solid being the coolest. Thus it melts during section B.)

The melting point is 60 °C.

18
Q

The heating curve (graph of temperature versus time) for a substance is shown.

What is the boiling point of the substance?

A

****(The substance is a solid to begin with because there are only three states of matter with solid being the coolest. Thus it boils during section D.)

The boiling point is 130 °C.

19
Q

What is the definition of the term pressure?

A

Pressure is defined as the Force per unit Area.

20
Q

p = F/A

(Define symbols and units)

A

p = pressure (Pa)

  F = Force (N)

A = Area (m^2)

21
Q

Example

Calculate the pressure exerted by a 20 kg box with a base measuring 20 cm by 30 cm.

A
p = ?
F = W = mg = 20 x 9.8 = 196 N
A = 20cm x 30xm = 0.2m x 0.3m = 0.06 m<sup>2</sup>
*p = F/A
p = 196/0.06
p = 3270 Pa (to 3 sig fig)*
22
Q

Explain how a snowshoe works

(in terms of pressure, force and area).

A

A snowshow spreads a Force (F) over a larger Area (A) - this causes the pressure (p) on the snow to decrease, since p = F/A.

23
Q

Account for the pressure of a gas, in terms of the particle model or kinetic theory of an ideal gas.

A
  • The particles of a gas are in constant random motion
  • and will collide with the container walls.
  • Each collision contributes a small amount of force.
  • The pressure = Total Force/Area.

(The Area being that of the container walls).

24
Q

State the relationship between pressure and Volume for a fixed mass of gas at constant temperature.

A

pV = constant

25
Q

p1V1 = p2V2

(Define symbols and units)

A

p - pressure (Pa)

V - Volume (m^3)

Other units can be used if consistent on both sides.

26
Q

Example

A gas container has a volume of 20 cm^3 at atmospheric pressure (1.01 x 10^5 Pa). Calculate the pressure inside when it expands to a volume of 1000 cm^3

A
p<sub>1</sub> = 1.01 x 10<sup>5</sup> Pa
V<sub>1</sub> = 20 cm<sup>3</sup>
p<sub>2</sub> = ?
V<sub>2</sub> = 1000 cm<sup>3</sup>

p1V1 = p2V2
1.01 x 105 x 20 = p2 x 1000
p2 x 1000 = 1.01 x 105 x 20
p2 = 1.01 x 105 x 20 / 1000
p2 = 2.02 x 103 Pa

27
Q

State the relationship between pressure and temperature for a fixed mass of gas at constant volume.

A

p/T = constant

28
Q

Explain what is meant by the absolute zero of temperature.

A

Absolute zero is the temperature (0 K) at which an ideal gas exerts zero pressure and occupies zero volume.

This is because it is the temperature at which the gas particles have no kinetic energy and stop moving.

29
Q

Describe how to convert a temperature in °C into K.

A

(Reminder: 0 K = -273 °C)

To convert a temperature from °C into K, add 273.

30
Q

Describe how to convert a temperature in K into °C.

A

(Reminder: 0 K = -273 °C)

To convert a temperature from K into °C, subtract 273.

31
Q

p1/T1 = p2/T2

(Define symbols and units)

A

p - pressure (Pa)

T - temperature (must be K)

Other units for p can be used if consistent on both sides.

32
Q

An aerosol can at room temperature (20 °C) contains gas at a pressure of 1·5 x 10^5 Pa. Calculate the temperature when the can is sprayed and the gas emitted is at atmospheric pressure (1·01 x 10^5 Pa).

A
p<sub>1</sub> = 1·5 x 10<sup>5</sup> Pa
T<sub>1</sub> = 20 °C = 20+273 = 293 K
p<sub>2</sub> = 1·01 x 10<sup>5</sup> Pa
T<sub>2</sub> = ?

p1/T1 = p2/T2
1·5 x 105/293 = 1·01 x 105/T2
Cross Multiply
1·5 x 105 x T2 = 1·01 x 105 x 293
T2 = 1·01 x 105 x 293 / 1·5 x 105
T2 = 197 K
(NB leave in K unless the question specifically asks for the answer in °C)

33
Q

State the relationship between volume and temperature for a fixed mass of gas at constant pressure.

A

V/T = constant

34
Q

V1/T1 = V2/T2

(Define symbols and units)

A

V - volume (m3)

T - temperature (must be K)

Other units for V can be used if consistent on both sides.

35
Q

A gas is held in a flexible container so that its pressure is constant. It has an inital volume of 400 m^3 and an inital temperature of 40 °C. What temperature would be required to double this volume?

A
V<sub>1</sub> = 400 m<sup>3</sup>
T<sub>1</sub> = 40 °C = 40 + 273 = 313 K
V<sub>2</sub> = 2 x 400 = 800 m<sup>3</sup>
T<sub>2</sub> = ?

V1/T1 = V2/T2
400/313 = 800/T2
Cross multiply
400 x T2 = 800 x 313
T2 = 800 x 313 / 400
T2 = 626 K

(NB leave in K unless the question specifically asks for the answer in °C)

36
Q

pV/T = constant

(Define symbols and units)

A

p - pressure (Pa)

V - volume (m3)

T - temperature (must be K)

Other units for p and V can be used if consistent on both sides.

37
Q

A 250 ml aerosol can at room temperature (20 °C) contains gas at a pressure of 5·0 x 10^5 Pa. Calculate the temperature when the can is sprayed to empty and 1000 ml of gas is emitted at atmospheric pressure (1·01 x 10^5 Pa).

A
p<sub>1</sub> = 5·0 x 10<sup>5</sup> Pa
V<sub>1</sub> = 250 ml
T<sub>1</sub> = 20 °C = 20 + 273 = 293 K
p<sub>2</sub> = 1·01 x 10<sup>5</sup> Pa
V<sub>2</sub> = 1000 ml
T<sub>2</sub> = ?

p1V1/T1 = p2V2/T2
5·0 x 105 x 250/293 = 1·01 x 105 x 1000/T2
Cross Multiply
5·0 x 105 x 250 x T2 = 1·01 x 105 x 1000 x 293
T2 = 1·01 x 105 x 1000 x 293 / 5·0 x 105 x 250
T2 = 237 K
(NB leave in K unless the question specifically asks for the answer in °C)

38
Q

Explain, in terms of particles, what happens to the pressure of a gas when its volume is increased?
(The mass and temperature of the gas are fixed.)

A
  • When the volume of a gas is increased, the particles have more space to move around in
  • The particles collide with the container walls less frequently
  • The total force on the walls decreases and because pressure = Force/Area, the pressure decreases and the area increases.
39
Q

Explain, in terms of particles, what happens to the pressure of a gas when its temperature is increased?
​(The mass and volume of the gas are fixed.)

A

* *When the temperature of a gas is increased, the particles gain kinetic energy i.e. move faster
The particles collide with the container walls more frequently and with g
reater force**.
The total force on the walls increases and because pressure = Force/Area, the pressure increases
as Area is constant.

40
Q

Explain, in terms of particles, what happens to the volume of a gas when its temperature is increased?
​(The mass and pressure of the gas are fixed.)

A

***** When the temperature of a gas is increased, the particles gain kinetic energy i.e. move faster.
* The particles collide with the container walls more frequently and with greater force
* The total force on the walls increases but the container is flexible so it expands i.e. the volume increases.