Book 1 (chapter 1: Temperature And Heat Transfer) Flashcards
What are fixed points?
Well-defined and reproducible temperature in the laboratory
Two types of fixed point
- Upper fixed point (steam point) (100 degree Celsius)
= boiling point of pure water at standard atmospheric pressure (1 atm) - Lower fixed point (ice point) (0 degree Celsius)
= melting point of pure ice at standard atmospheric pressure (1 atm)
(Not international standard used by scientist)
Internal energy (definition)
Sum of molecular kinetic energy due to random motion and molecular potential energy.
Heat (definition)
Energy transferred between two bodies due to temperature difference
Symbol: Q
Unit: J
Molecules collide with each other. Energy is transferred by collisions.
Heat capacity (definition)
Energy required to change the temperature of an object by 1 degree Celsius
Heat capacity (definition)
Energy required to change the temperature of an object by 1 degree Celsius
Absolute zero (0K=-273degree celcius)
Particles freeze and do not move
Relationship between the avg KE and temperature
When the molecules posses more kinetic energy and move more rapidly, the temperature of the body increases
Two bodies at the same temperature
Same average molecular kinetic energy
BUT the one with larger mass has a higher internal energy
Temperature (definition)
It is a measure of the average kinetic energy due to the random motion of the molecules in a body
Relationship between internal energy AND temperature and mass
Since the internal energy of a body includes the total kinetic energy of all the molecules in the body. It increases with temperature and mass.
Energy transfer
The larger the temperature difference, the higher the rate of energy transfer.
Heat flows from a high-temperature body to a low-temperature body
The energy transfer stops when they reach the same temperature (thermal equilibrium)
How to increase internal energy of a body?
Increase the temperature through HEATING and DOING WORK
Conduction (s,l,g) (have to be in contact)
Molecules vibrate (x move)
Heat conduct from warm to cold
Explanation: particles on the hotter end vibrate faster and hit neighbouring particles which then gain energy through collisions and vibrate faster. Energy is transferred from hotter to colder end by collisions of particles.
(Vacuum: no conduction)
The material which conducts heat fast is called thermal conductor (or conductor of heat)
The material which conducts heat slow is called thermal insulator (or insulator of heat)
Why is metal a better thermal conductor than non-metal?
They have free electrons which can move freely and help transfer heat.
How does loathes keep us warm?
The clothes trap air which is a good thermal insulator
Why do you feel colder when you touch a metal plate when you touch a wooden plate?
Metal is a better thermal conductor and it transfers heat faster than wood.
Why are most of the cookware made of metal?
Because metal is a good thermal conductor and transfers heat faster.
Why some of the cookware is made of clay?
Because slay is a good insulator which can reduce heat loss and ensures more even heating.
Why are the ice cubes at the bottom seem not to be letting while the surface on the surface is boiling?
Because water is a good thermal insulator and heat only transfers slowly to the bottom by conduction.
convection only occurs at the bottom
Order of thermal conductivity
Solid > liquid > gas
Convection (concepts)
Definition: it is a heat transfer process by means of movement of molecules within fluid (gas or liquid), that arises through difference in density.
Process: Water heats up, hot water rises and becomes less dense. Cold water sinks.
Convection does not happen in solid
Examples and application of convection
- Sea breeze
Because the specific heat capacity of water is larger than land, in daytime, temperature of water is smaller than land and breeze from sea to land; while at night time, temperature of water is larger than land and breeze is from land to sea. - Heater and air-conditioner
Air condition is set up high on the wall. It takes in the warm air and cools it. This facilitates the convection current.
Heater is placed on the floor . It takes in the cold air and warm it, this facilitates the convection current. - The shapes of a candle flame
Hot air rises, and cool air sinks. - Convection in the Earth (for geography ONLY)
- Freezers in the supermarket
Cold air sinks and remains in the freezer - Igloo
Snow is a good thermal insulator and it traps a lot of air. It can reduce heat loss due to convection and conduction. Hot air is trapped inside the igloo.
Prior knowledge of radiation
Why does black objects look black?
—> Black object absorbs all the light and reflect no light.
Why does white object looks white?
—> White object absorbs no light and reflect all light.
Why does red object look red?
—> Red object absorbs all light except red and reflect red light.
The 7 colours of the rainbow: red, orange, yellow, green, blue, indigo, violet
Radiation (concept)
Every object emits radiation in all directions.
The hotter the object, the more infrared-red radiation it emits.
Everything is both an absorber and radiator/emitter of radiation.
A object colder than surrounding has a net gain of energy by radiation.
A object hotter than surrounding has a net loss of energy of radiation.
Factors affecting the emission and absorption or radiation
- Temperature: the higher the temperature, the more radiation it emits
- Colour: Dull black surface is a good absorber and emitter of radiation. Black objects look black at room temperature. Shiny /white surfaces are poor absorber and radiator / emitter of radiation.
- Surface area: the larger the surface area, the more radiation it emits.
How to distinguish if something is related to conduction/convection/radiation?
Conduction: material
Convection: 👍🏻fan/👎🏻cap/cover
Radiation: colour
—> increase / decrease the heat transfer by ______________ (gain / loss)
Applications of heat transfer
- Vacuum flask
Cap (traps the hot air inside (if hot liquid) —> reduce the heat transfer by convection
Plastic cup (good thermal insulator —> reduce the heat loss by conduction)
Silvered surfaces (silver is a poor absorber of radiation reduce heat transfer by radiation) - Pressure cooker
Lid seals shut trapping steam inside (reduce heat loss by convection)
Trapped s team builds pressure and raises cooking temperature (it has higher air pressure than outside)
Higher pressure —> higher boiling point of water —> food is cooked at a higher temperature - Greenhouse
Infra-red radiation cannot potassium through the glass - Summer and winter uniform
In summer time, white is a poor absorber of radiation. In winter, dark grey i s a good absorber of radiation - Halogen lamp cooker
Lid with fan and halogen bulb —> cook more evenly (more air flow) - Solar cooker
Temperature (definition)
The measure of average molecular kinetic energy per molecule
Molecular potential energy
The larger the distance between the molecules, the larger the potential energy
Molecular potential energy
The larger the distance between the molecules, the larger the potential energy
Why is the energy of 1kg ice smaller than 1kg water?
Their temperatures are the same and they have the same average kinetic energy. However, objects at liquid state larger potential energy than that in solid state. Water has a higher potential energy than ice. That’s why the internal energy of water is larger.
Change in temperature vs change in state
When ice melts, the temperature remains the same
