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The rope ladder of a boat hangs over the side of the boat and just touches the water. The ladder rungs are 8 inches apart. How many rungs will be under the water when the tide rises 3.5 feet?
A. 1 rung
B. 2 rungs
C. 5 rungs
D. 0 rungs
How much heat would need to be added to a 2.5 kg sample of water in order to increase the temperature from 35oC to 95oC? (Remember Q
= mcΔT) cwater = 4190 J/kgoC
A. 366.6 kJ
B. 628.5 kJ
C. 995.1 kJ
D. 1361.8 kj
Because the rubber ball’s temperature increased faster than the banana dipped in LN2, that means which had a higher specific heat.
A. The rubber ball
B. The banana
C. Both have the same
D. Neither are capable for getting heat
Pre-AP Physics Unit 5: Thermodynamics
“Thermodynamics”
Is derived from Greek meaning “movement of heat.”
The First Law of Thermodynamics
Official Definition:When heat flows in or out of a system, the energy it gains or loses is equal to the amount of heat transferred.
Or… Heat = Energy !
Is analogous to the Law of Conservation of Energy
We are now dealing with Internal Energy
Temperature:
What is it? How “Hot” or “Cold” a substance is.
Temperature represents the average translational kinetic energy of the individual particles in a system.
The Temperature Scales Fahrenheit – water freezes at 32oF and boils at 212oF
Celsius – Water freezes at 0oC and boils at 100oC
Kelvin – is based off of Absolute Zero
Absolute Zero So cold that all particles stop moving!
Total energy of the particles is 0.
Temperature:
Temperature Conversions Celsius to Fahrenheit
Fahrenheit to Celsius
Celsius to Kelvin
Examples
A piece of metal is heated to 475 oF, what is this temperature in Celsius?
A. 887 oC
B. 246 oC
C. 519 oC
D. -27 oC
The melting point of copper is 1073 oC. What is this temperature in Kelvin?
A. 800 K
B. 1899 K
C. 578 K
D. 1346 K
Specific Heat Capacity
What is it? The resistance to change in temperature of a substance.
The Equation: Q = mcΔT
Examples:
How much heat energy is required in order to raise the temperature of a 0.5 kg iron nail from a temperature of 25oC to 80oC?
A. 5750 J
B. 18400 J
C. 12650 J
D. 24150 J
A 75 kg piece of a concrete sidewalk on a sunny day will gain about 650,000 Joules of heat energy from the sun. By how much will its temperature increase on that day?
A. 25133333 K
B. 3.0 K
C. 16810 K
D. .33 K
An iron pot containing 5 kg of water at an initial temperature of 23oC is placed on a stove. If the stove applies 560,000 Joules of heat energy, what is the final temperature of the water?
A. 49.7 oC
B. 26.7 oC
C. 3.7 oC
D. 76.5 oC
A cup of water (c=4190) and a piece of metal (c=350) are both left to sit out on a sunny day. By the end of the day, which will have a greater change in temperature?
A. water
B. metal
C. They will have same temperature
D. I don’t know
The Second Law of Thermodynamics Official Definition:
Heat, of itself, never flows from a colder object to a warmer object.
Energy always flows from Hot to Cold
This law is also called the Law of Entropy
What is Entropy?
The amount of disorder in a system
The universe is always moving towards more entropy
Examples: Ice melting
Liquid water evaporating
It takes Work (energy) to decrease Entropy
Types of Heat Transfer
Conduction Heat transfer between materials that are in direct contact
with each other.
Convection Transfer in a fluid by movement of the substance itself.
Radiation Energy transmitted by electromagnetic waves.
Phase Changes
The States of Matter:
Phase Changes
Types of Phase Changes: Melting
Evaporation
Condensation
Boiling
Sublimation
Melting
Condensation
EvaporationBoiling
Sublimation
Phase Changes
How do you change the melting point or boiling point of a substance? Add a solute
Change the pressure
Phase Changes
Energy During Phase Changes
What happens to the temperature of water as heat is added?
It Increases.
What happens to the temperature during a phase change?
It remains constant.
Phase Changes
Latent Heat Latent Heat of Fusion
The amount of energy required to change a unit mass of any substance from a solid to a liquid (and vice versa).
Abbreviated Lf (or Hf)
Latent Heat of Vaporization
The amount of energy required to change a unit mass from liquid to gas (and vice versa).
Abbreviated Lv (or Hv)Lv
Lf
Phase Changes
Latent Heat
Equation:Q = mL
Where:Q = heat added during phase changem = mass of sampleL = Latent Heat (of fusion or vaporization)
Examples:
How much heat is required to boil 3.5 kg of water? (Lv = 2.26x106 J/kg)
A. 7910 J
B. .0001264 J
C. .0000001264 J
D. 7910000J
An experiment is performed and it is found that it takes 13.0 x 106 Joules of energy to melt 4.8 kg of iron. What is the Latent Heat of fusion for Iron?
A. 2.7 x 106 J/kg
B. 2.7 x 103 J/kg
C. 6.2 x 107 J/kg
D. 6.2 x 104 J/kg
Latent Heat of Fusion
Lf