Thermodynamics

Question 1

Equation for internal energy of a system?

Answer 1

U = w + q

Internal energy = work + heat

Question 2

What is kinetic energy?

Answer 2

E = mv^2

A particle with both mass and velocity

Question 3

Name 2 types of potential energy.

Answer 3

1. Gravitational potential

2. Chemical bond energy (energy stored in chemical bonds

Question 4

What happens to the energy during bond formation and bond cleavage?

Answer 4

Bond formation releases energy

Bond cleavage requires energy

Question 5

What is an open energy system?

Answer 5

A system where both matter and energy can be transferred between the system and the surroundings

Question 6

What is a closed energy system?

Answer 6

A system where only energy can be transferred between the system and the surroundings

Question 7

What is an isolated system?

Answer 7

A system where neither matter nor energy can be transferred between the system and the surroundings

Question 8

What is the 1st law of thermodynamics and what does it state?

Answer 8

Conservation of energy - energy cannot be created or destroyed and can only be transformed between different forms.

Question 9

What is work?

Answer 9

Any process that can be used to lift a weight

Question 10

How does work affect energy transfer?

Answer 10

Energy is transferred from the system to its surroundings

Question 11

What is the equation for work?

Answer 11

Work = force x distance

Question 12

What is the equation for force?

Answer 12

Force = mass x acceleration
Force = k x q1 x q2 / r^2

k = coulombs, q = magnitudes of the charges (+ or -), r = distance between charges

Question 13

What happens when a hot system comes in contact with a colder surround and vice versa?

Answer 13

The hot system will spontaneously get colder however the reverse will not happen and so the cold system will not get colder

Question 14

What is the equation for energy derived from pressure and volume changes?

Answer 14

Energy = pressure x volume

Question 15

What is enthalpy?

Answer 15

In thermodynamics, it’s a measure of the heat content of a chemical or physical system

Question 16

What is the equation for the enthalpy of a system?

Answer 16

H = U + pV

H = enthalpy/heat, U = internal energy, p = pressure, V = volume

Question 17

What is the definition of the change of enthalpy?

Answer 17

△H = △U + p△V

H = enthalpy/heat, U = internal energy, p = pressure, V = volume

Only the change in volume is important as in chemistry most measurements are made at constant pressure.

Question 18

What happens in an endothermic reaction?

Answer 18

Energy is absorbed from surroundings to break bonds

△H > 0

Question 19

What happens in an exothermic reaction?

Answer 19

Energy is released into the surroundings from bond formation

△H < 0

Question 20

What is Hess’s law?

Answer 20

Hess’s law states that the enthalpy change for a chemical reaction is independent of the route taken. This means that the enthalpy change for the overall process will be identical regardless of how many steps are taken

Question 21

What is used to measure enthalpy changes?

Answer 21

A bomb calorimeter