Chapter 2 Flashcards
What does Internal Energy consist of?
- Kinetic Energy
of particles due to their RANDOM MOTION - Potential Energy
due to the INTERACTIONS BETWEEN PARTICLES
What does the Kinetic Energy consist of?
- Translational
- Rotational
- Vibrational (within particles)
What is temperature?
Measure of the average translational kinetic energy of the particles within a system, because, at any instant in time, the particles within a system will have a RANGE of speeds, THUS A RANGE OF KINETIC ENERGIES.
How do you convert Celsius to Kelvin
Add 273.15
When does water boil in Kelvin?
373.15
When does water freeze in Kelvin?
273.15
Difference between heat and temperature?
Heat is a measure of the TRANSFER OF THERMAL ENERGY
Temperature is the measure of the average translational kinetic energy of the atoms
Summarise Internal Energy
It describes the energy associated with the motion and interactions between particles in a system, AKA Thermal energy
What is the kinetic theory of matter?
ALL MATTER consists of particles that are CONSTANTLY MOVING in a RANDOM WAY
What is Thermal Equilibrium
When two systems have the same temperature, and there is no net heat transfer
What is heat?
The energy the flows between systems due to the difference in temperature
What is Heat written as and measured in?
Written as Q, measured in Joules since its ENERGY
What is conduction?
form of heat transfer between systems due to collisions between their particles
Conduction only occurs when…?
- The two systems are in direct physical contact
- The systems are at different temperatures
What does the heat transfer rate formula tell us?
It tells us that the heat transfer rate between 2 systems is directly proportional to their difference in temperature, as Q/T is directly proportional to the change in temp.
What happens to the rate of conduction if the area increases?
Also increases
Summarise what happens when 2 systems are in physical contact
Particles collide and exchange translational kinetic energy (temperature), and in each collision, the temperature is transferred from the particle with more temp to the one with less
Over time, energy transfers from the higher temp system to the lower temp system
Give an example of a good thermal conductor
pure metals, such as diamond (best) are good conductors of heat as they are closely packed together, and have free moving electrons thus collide more
Give an example of a good thermal insulator
air is a good insulator as the particles are more spaced out and they dont collide very often, meaning the heat transfer rate is very slow
How is heat transferred through convection?
As higher temperatures means that the particles have greater average kinetic energy, meaning that this additional kinetic energy results in the partciles being more SPACED OUT, DECREASING THE DENSITY OF THE MATERIAL.
The fluid with the higher density SINKS, DISPLACING the LESS DENSE FLUID, PUSHING the LESS DENSE fluid UPWARDS
When can convection occur?
Only in flowing substances (FLUIDS)
It can be natural or forced.
Summarise convection in a pot
The colder fluid is denser, so it sinks pushing up the hotter fluid. As the hotter fluid cools down after RISING, it TRANFERS HEAT TO ITS COOLER SURROUNDINGS, THUS increasing the density and thus falling to the bottom, this cycle keeps going as long as heat persists.
What is forced convection?
Fluid flow that transfers thermal energy where the heat itself does not drive the flow, meaning that ANOTHER energy source must drive the flow
What is thermal radiation?
Form of heat transfer that is due to the emission & absorption of energy as electromagnetic radiation
How is heat transferred through thermal radiation?
Charged particles emit electromagnetic radation whenever they accelerate, and when they accelerate while vibrating and colliding, some of the translation kinetic energy is transformed into electromagnetic radiation, causing a decrease in the internal energy and temperature
What happens when radiation meets an object or substance?
- Transmitted
- Reflected
- Absorbed
If Q is negative, that means that energy is being what?
Released rather than absorbed
What is latent heat?
The energy that is absorbed or released when a substance undergoes a change in state. The temperature remains constant
Explain what happens during the changes in state of matter
- The TEMPERATURE remains CONSTANT
- The energy that is absorbed or released is LATENT HEAT, also “Hidden heat”, meaning it is hidden as potential energy, which is used to create and break bonds between the atoms
- Latent Heat has no effect on the temperature of the particles
Describe heating curves
As more heat is absorbed, the temperature increases
- The temperature stays constant during a state change, and only changes after the state change
- the samr amount of thermal energy that must be absorbed to boil a liquid into a gas is the same as how much is released when the gas condenses
Explain why gas condensing is a negative latent heat quantity
Because releasing energy is a negative quantity
Define Evaporative Cooling
The process of particles in a liquid escaping to the top of the surface
Why does evaporative cooling occur
Because higher-energy particles constantly escape from its surface, reducing the temperature, making the liquid cooler.
The rate of evaporative cooling is greater when…
- The temperature of the liquid is greater to begin with
- The surrounding air is drier
- Air moves over the liquid surface (wind)
- SUrface area is larger
- the liquid has a lower boiling point
Explain evaporative cooling
When a liquid evaporates, it cools its surroundings.
- Higher kinetic energy particles escape from the liquid surface to the air throughevaporation
- the remaining particles in the liquid now have a lower temperature than before
- meaning that more heat continues to be transferred from the surroundings t the liquid
