19 Thermal Physics

Question 1

what is the internal energy of an object?

Answer 1

the energy of its molecules due to their individual movements and positions
ALSO
the sum of the random distributions of the kinetic and potential energies of its molecules

Question 2

what is thermal energy?

Answer 2

the internal energy of an object due to temperature

Question 3

how is the internal energy of an object increased?

Answer 3

• energy transfer by heating
• work done on the object

Question 4

how does the internal energy of an object stay constant?

Answer 4

• there is no energy transfer by heating and no work done
• energy transferred by heating and work done balance each other out

Question 5

what is the first law of thermodynamics?

Answer 5

the chance of internal energy of the object = the total energy transfer due to work done and heating

Question 6

what are the characteristics of the structure of a solid?

Answer 6

• atoms and molecules are held to each other by forces due to electrical charges of protons and electrons in the atoms.
• the molecules vibrate randomly about fixed positions
• higher temperature = more vibration and increased kinetic energy of molecules

Question 7

what happens when a solid melts?

Answer 7

the molecules vibrate so much that they break free from each other and the substance loses shape

Question 8

what are the characteristics of the structure of a liquid?

Answer 8

• the molecules move about at random in contact with each other
• the forces between molecules are not strong enough to hold them in fixed positions

Question 9

what are the characteristics of the structure of a gas or vapour?

Answer 9

• molecules move about randomly but much further apart on average than a liquid

Question 10

what is temperature?

Answer 10

a measure of the degree of hotness of the object

Question 11

what is thermal equilibrium?

Answer 11

when no overall heat transfer occurs between two objects at the same temperature

Question 12

how is a temperature scale defined?

Answer 12

in terms of fixed points (standard degrees of hotness that can be accurately reproduced)

Question 13

How is the Celsius scale defined?

Answer 13

1. ice point, 0 degrees C, which is the temperature of pure melting ice
2. steam points, 100 degrees C, which is the temperature of steam at standard atmosphere pressure

Question 14

how is the absolute scale defined?

Answer 14

1. absolute zero, 0K, the lowest possible temperature
2. the triple point of water, 273.16 K, which is the temperature at which ice, water and water vapour co-exist in thermodynamic equilibrium

Question 15

how do you convert from kelvins to degrees C?

Answer 15

C = K - 273.15

Question 16

what is absolute zero?

Answer 16

the lowest possible temperature
- objects at absolute zero have minimum internal energy

Question 17

what is specific heat capacity?

Answer 17

the energy needed to raise the temperature of a unit mass of the substance by 1 K without change of state