MNSR23 Flashcards
What is the mechanism required to change temperature
heat energy must be either added or removed
What does the rise in T depend on
1- mass
2- Specific heat capacity
Specific Heat capacity formula
Q = m C (delta)T
Q being the amount of heat energy required
Define specific heat capacity
amount of heat energy required to change the temperature of 1kg of a substance by 1C
Define thermal inertia
measure of how quickly or slowly an object gains or loses heat to its environment
Explain the thermal inertia of water and steel
- Water (and the body) have high thermal inertia
- High thermal inertia is said to be great resistance to a change in temperature
- Steel has a low thermal inertia
(Work out): How much heat is required to raise the temperature of a 20kg iron from 10oC to 90oC
( specific heat of iron C= 450 J/Kg.oC
Q = mC(delta)T
Change in Temp. (delta)T= (90-10) =80 C
Q= 20 x 450x 80 = 7.2 x105 J = 720
State the 5 states of matter
1- solid 2- liquid 3- gas 4- plasma 5- Bose-einstein condensate
Explain the chemical bonding of SOILDS and their properties
- Particles are tightly packed together
- Vibrate about a fixed position
- Have a definite shape and volume
- infinite number of free surfaces
- Metallic solids dont need all their electrons for bonding
- insulators need all their electrons for bonding
Explain the chemical bonding of LIQUIDS and their properties
- particles of liquids are tightly packed but free to move around
- indefinite shape but definite volume
- one free surface
Explain the chemical bonding of GASES and their properties
- Particles of gases are very far apart and move freely
- interact with each other by elastic collisions
- indefinite shape and indefinite volume
- No free surface
Explain the structure and properties of PLASMA
- Ionized gas
- Very good conductor of electricity and affected by magnetic fields
- indefinite shape and volume (similar to gases)
Explain the properties of BOSE-EINSTEIN CONDENSATE
- a state of matter of a dilute gas of bosons cooled to temperatures very close to absolute zero
- opposite of plasma
- occurs at ultra low temperatures, at a point where the atoms are not moving at all
Describe a way of phase changes
- The four interchangeable states can be achieved : liquid gas solid and plasma
- This is done by increasing temperature to lead to phase changes
- Solid > Liquid > Gas > Plasma
List the 4 phase chase changes
1- Freezing
2- Melting
3- Boiling
4- Evaporation
(Refer to graph on page 16): Describe
Add heat to block of ice. Temp. rises until a Phase Change occurs. Temp. stays constant until all ice changes (water) and temp. rises until all water boiling and stays const. until all water changes to (steam)
What is latent heat
amount of heat absorbed or released
Define and give formula for LANTENT HEAT OF FUSION
- The energy (heat) required to convert 1kg of solid to 1 kg of liquid
- Q= m Lf
- Lf=344 kJ/kg
Define and give formula of Latent heat of Vapourisation
- The energy (heat) required to convert 1kg of liquid to 1 kg of gas
- Q= m Lv
- Lv= 2260 kJ/kg
Describe the evaporation of water in comparison to ice
Water takes more energy to evaporate than ice to melt
When each molecule of water evaporates from skin it take a significant amount of heat energy
(Work out):How much energy does a refrigerator have to remove from 1.5 kg of water from 20oC to make ice at -12oC.
Q= mCwDT+ mLf+ mCiceDT
Q= 1.5x4186x(20-0)+1.5x3.34x105+ 1.5x2100x(0-(-12))
Q=
Define Triple Point
- the triple point of a substance is the temperatures and pressure at which three phases (for example, gas. Liquid and solid of that substance coexist in thermodynamic equilibrium
- For water at exactly 273.16K (0.01 oC and a partial vapour pressure of 611.73 Pascal
State the 4 modes of heat transfer
1- Conduction (solids)
2- Convection (liquids and gases)
3- Radiation (air/vaccuum)
4- Evaporation (sweating)
- Convection and Radiation are losses from exposed surface of body
- Conduction is heat losses through covered surface parts of body
