Chapter 9 Thermodynamics

Question 1

What is the internal energy of a substance due to?

Answer 1

The kinetic energy of the particles from their vibrations/movement and the potential energy holding them together

Question 2

How do internal energies change depending on state?

Answer 2

In solids - the internal energy is due from vibrating particles and the potential energy from the bonds.
These bonds are weaker in liquids and so the potential energy is smaller and in gases, there are no almost no forces of attraction between particles and the internal energy is almost entirely due to the kinetic energy of the particles

Question 3

What is temperature a measure of?

Answer 3

The kinetic energies of the particles in a substance

Question 4

What is heat?

Answer 4

Heat is the flow of thermal energy

Question 5

How does heat flow?

Answer 5

It flows from a high temperature to a low temperature

Question 6

What do we say if two objects are the same temperature?

Answer 6

They are in thermal equilibrium and no thermal energy flows

Question 7

What does an object having a high temperature mean?

Answer 7

The particles are moving / vibrating with higher average speeds than a substance at a lower temperature

Question 8

What is absolute zero?

Answer 8

A theoretical temperature (0K) where pressure is 0 and particles stop moving completely - a point of minimum internal energy

Question 9

How do you convert from C to K?

Answer 9

K = C + 273.15

Question 10

What is the specfic heat capacity equation?

Answer 10

ΔE = mcΔθ

Question 11

What is specific heat capacity?

Answer 11

The energy required to raise the temperature of 1kg of a substance by 1 degree C/K

Question 12

What is specific heat capacity measured in?

Answer 12

Jkg−1K−1

Question 13

Describe what happens to the energy of a solid being heated and melting?

Answer 13

The solid is heated which means energy is transferred to the particles making them vibrate more, increasing their kinetic energy and the temperature of the solid. Potential energy stays constant

At melting point, the particles do not vibrate any quicker, meaning the kinetic energy and temperature are constant. The bonds that keep the particles in a rigid shape are broken and the potential energy increases

Question 14

What is the difference in terms of energy between melting and boiling point?

Answer 14

Boiling point takes much more energy to ‘overcome’ as all the bonds holding the particles together need to be broken as opposed to the structural bonds that are broken at melting point

Question 15

What is the specific latent heat equation?

Answer 15

E = ml
where l is the SLH

Question 16

Define specific latent heat?

Answer 16

The amount of energy required to change the state 1kg of a substance

Question 17

What are the units of specific latent heat?

Answer 17

J kg-1

Question 18

What is the energy required to change 1kg of a substance of solid into liquid?

Answer 18

Specific latent heat of fusion

Question 19

What is the energy required to change 1kg of a substance of liquid into gas?

Answer 19

specific latent heat of vaporisation

Question 20

What is Boyle’s Law?

Answer 20

For a fixed mass of gas, the pressure is inversely proportional to its volume when kept at a constant temperature

Question 21

What is the equation for Boyle’s Law?

Answer 21

p ∝ 1/V for a constant T

Question 22

What is Charles’s Law?

Answer 22

For a constant mass of gas at a constant pressure, the volume occupied by a gas is proportional to its absolute temperature. All gases expand at the same rate when heated

Question 23

What is the equation for Charles’s Law?

Answer 23

V ∝ T for a constant p

Question 24

What is the Pressure Law?

Answer 24

For a constant mass of gas at a constant volume, the pressure exterted by the gas is proportional to its absolute temperature

Question 25

What is the equation for the Pressure Law?

Answer 25

p ∝ T for a constant V

Question 26

Give 5 properties of ideal gases?

Answer 26

• Molecules have negligible size
• Molecules are identical
• All the collisions are perfectly elastic
• Molecules exert no forces on each other apart from collisions
• The motion of the molecules is random

Question 27

What is the equation we can form by combining the gas laws for an ideal gas? What does each letter represent?

Answer 27

pV=nRT
where p=pressure, V=volume, n=number of moles, R=universal gas constant, T=temperature

Question 28

What is another form of the ideal gas equation without number of moles?

Answer 28

pV =NkT
N = no of molecules
k = boltzman constant