Thermodynamics Flashcards
1
Q
Solid particles
A
-closely packed, regular structure, strong forms of attraction, vibrate about fixed positions
2
Q
Liquid particles
A
-touching, irregular structure, random motion
3
Q
Gas particles
A
-far apart, no fixed position, move randomly, rapid motion
4
Q
Particles
A
The hotter a material is, the faster its particles move. It possessed more internal energy than a colder material due to it having a greater total kinetic energy
5
Q
Smoke particle (Brownian motion)
A
- If you look at smoke through a microscope you will see particles moving in a zig zag random motion.
- Smoke particles have very little mass but are large enough to be seen.
- Their random motion explained by the fact they are colliding tight he invisible small air particles, which are also moving randomly but faster
6
Q
Density
A
- Solids, liquids and gases have different properties and characteristics. One of which is density.
- Solids often are very dense, liquids are less so and gases haver very low densities
- Density (P) is how much mass (m) something has for a certain volume (v), in other words how ‘squashed up’ its particles are or how heavy something is for its size
- Density= mass/ volume
- Mass= density x volume
- Volume= mass/ density
7
Q
temperature and changing state
A
- Hotter objects have more internal energy
- Temperature is a measure of the average kinetic energy of the particles in the object
- Particles in hotter objects are moving faster
- A hot bath has a lower temperature than a sparkler but has more internal energy because it has more particles
8
Q
Thermal expansion
A
- Solids, liquids and gases all expand upon heating because the atoms gain energy and vibrate more, causing them to become further apart (increases volume)
- Expansion is greatest in gases, then liquids and lowest in solids. This is because of the much weaker intermolecular bonds between particles
- Applications of thermal expansion include:
- The liquid in a thermometer expands and contacts when the temp changes
- To maintain constant temp at home, a bimetal thermostat is used. This consists of a metallic strip of 2 different metals which have different rates of expansion. When temp gets too high, the bimetal strip bends to make the contacts separate and switch off the heating. Once the temp falls enough, metal strip becomes straight again and the contacts touch, switching heat back on
9
Q
Measuring temperature
A
- Physical property of thermal expansion can be used for temp measurement using a liquid-in-glass thermometer
- As temp rises or falls, the liquid (mercury or alcohol) expands or contracts. The amount of expansion can be matched to a temp on the scale
- A thermistor thermometer probe contains a material that becomes a better electrical conductor when temp rises
- A thermocouple thermometer probe contains two different metals joined together to form two junctions: temp difference between junctions causes a tin voltage and a greater temp difference gives a greater current
10
Q
Thermocouple thermometer
A
- They are used for high temps which may change rapidly. They have a large range and can be connected to electrical circuits or computers
- To increase the sensitivity put liquid in a narrower tube
- Responsiveness can be increased by making glass bulb smaller
11
Q
Changing states
A
- Solid to liquid is melting
- Liquid to gas is evaporation
- Gas to liquid is condensation
- Liquid to solid is freezing
- Solid to gas is sublimation
- This happens when particles have enough energy to overcome forces between them
- Energy involved in making/ braking intermolecular bonds so that a change of state occurs is known as later heat. The temp remains constant
12
Q
Heat transfers
A
- Thermal energy will be transferred if there is a temp difference
- 3 main ways where thermal energy is transferred from a region of high temp to one at a lower temp; conduction, convection and radiation
13
Q
Thermal conduction
A
- Transfer of thermal energy through a substance without the substance itself moving
- Conduction happens because particles transfer energy to neighbouring particles. They then pass on this energy to other particles and so on
- Solids= better conductors
- Metals= good thermal conductors due to delocalised electrons
14
Q
Convection
A
- Main method of heat transfer in fluids/ liquids and gases
- Hot air above radiator will rise as it is less dense than the surrounding cool air. As it rises, cooler air from the opposite end of room will move in to take its place. Circulating currents/ convection current
15
Q
Radiation
A
- Conduction and convection need a substance but radiation is the transfer of energy by infrared (IR) waves. IR waves travel at the speed of light in a vacuum. This is how we receive heat from the sun
- All objects emit IR waves, can also be reflected and absorbed by different materials
- Best emitter: dull black -> shiny black -> white -> silver (worst)
