thermodynamics

Question 1

what is the first law of thermodynamics?

Answer 1

states that energy cannot be created or destroyed. it can only be converted from one form to another
total energy of a closed system remains constant

Question 2

what is the second law of thermodynamics?

Answer 2

systems will tend towards disorder
some energy is always lost or wasted - impossible for a system to be 100% efficient
Not all heat can be converted into useful work/ energy

Question 3

work?

Answer 3

work done is the energy transferred from one place to another

Question 4

work equation

Answer 4

W=F x distance
work in joules

Question 5

describe arrangement of particles in solid

Answer 5

tightly packed
vibrating in fixed positions
strong IM bonds
slow moving kinetic energy

Question 6

describe arrangement in liquid

Answer 6

IM forces are weaker
not as slightly packed
particles can flow or slide over another
less negative potential energy

Question 7

describe arrangement in gas

Answer 7

no potential energy
no IM bonding
fills entire container
rapid and random movement
higher kinetic energy

Question 8

define an ideal gas

Answer 8

modelled as a series of point particles randomly moving around the space colliding with each other and the walls of space

Question 9

what are the three variables that describe a gas in a box

Answer 9

pressure Nm-2 - collisions between particles and container walls
volume m3 - size of container
temperature K - average speed of molecules (kinetic energy)

Question 10

describe what would happen to pressure if a closed vessel eg glass bottle was placed over a flame?

Answer 10

due to heat increasing, particles would gain kinetic energy and collide more faster with other particles. pressure increases in closed vessel so the frequency and magnitude of collisions between container walls and particles increases

Question 11

adiabatic

Answer 11

there is no transfer of heat
temperature changes due to variations in internal energy (which changes when work is done on or by system).
expansion and compression occurs so quickly there is little time for heat to be exchanged with surroundings

Question 12

1st law of thermodynamics equation

Answer 12

AU = Q-W

Question 13

heat engine

Answer 13

allows heat to flow from a hot reservoir to a cold reservoir and converts heat into mechanical work energy to do work

Question 14

give equation for efficiency of general heat engine

Answer 14

efficiency = 1 - Q out / Q in

Question 15

define carnot cycle

Answer 15

ideal cycle of changing pressures and fluids

Question 16

internal energy

Answer 16

potential and kinetic energy combined - the sum of all energy of molecules

Question 17

isothermal

Answer 17

exchange of heat occurs to ensure temperature remains constant
to ensure system is in thermal equilibrium
TEMP DOES NOT CHANGE

Question 18

compression

Answer 18

reduced volume of gas
work is done on gas by piston

Question 19

expansion

Answer 19

increase in volume of gas
gas does work on piston

Question 20

ideal gas law equation

Answer 20

PV = NkT

Question 21

what is the value for Boltzmann constant

Answer 21

1.38 x 10 -23m2 kgs-2 K-1

Question 22

explain the stages of the carnot cycle

Answer 22

1. isothermal compression - piston does work on gas to reduce volume which increases pressure. slight increase in heat energy is given out to cold reservoir to keep temperature constant and ensure it does not change
2. adiabatic compression - working material is compressed adiabatically. piston does work on gas which decreases volume and increases pressure. Temp rises as work is done but there is no heat exchange with surroundings
3. isothermal expansion
   working substance expands isothermally and gas does work on piston as it expands and pushes out piston
   temp of gas remains constant and pressure drops slightly
   4.adiabatic expansion -
   working substance expands adiabatically
   pressure decreases and temp increases due to internal energy variations
   no heat is exchanged with surroundings and does work on surroundings

Question 23

what does the carnot cycle consists

Answer 23

4 reversible processes:
2 isothermal processes - constant temp
2 adiabatic processes - no heat exchange

Question 24

thermal equilibrium

Answer 24

No net transfer of thermal energy between them

Question 25

Thermal capacity

Answer 25

Specific heat capacity - energy required to change the temperature of 1kg of material by 1C