Thermodynamics Flashcards
Temperature definition
Thought of as the degree of hotness of an object. It indicates the direction of internal energy flow. It diffuses from high to low.
How are temperate scales formed?
Two standard degrees of hotness are chosen and called the fixed points. Numbers are assigned to them.
Celsius scale
Divided into 100 increments known as degrees °C.
Fahrenheit scale
Freezing point of water is 32° F and boiling point is 212° F.
Divided into 180 increments known as degrees ° F.
A Fahrenheit degree is 5/9ths as large as a Celsius degree.
Fahrenheit to Celsius
°C = (°F -32) / 1.8
Celsius to Fahrenheit
°F = (1.8 x °C) + 32
What is absolute zero?
0 K = -273°C
Celsius to Kelvin
Tk = Tc +273
The freezing point of water is 273K, and boiling point is 373K
Fahrenheit to Rankine scale
Tr = Tf + 460°
The freezing point of water on the Rankine scale is 492°R, boiling point is 672°R.
What is Heat (Q)?
Heat (Q) is a form of energy that when added to a body, increases the internal energy content of the body, causing a rise in temperature.
What is the S.I. unit for heat?
Joule (also Kcal)
What is heat capacity (c) ?
Defined as the ratio of heat supplied to an object or specimen to its consequent rise in temperature. The unit is JK^-1.
What is specific heat capacity (c)?
Defined as the heat energy required to increase the temperature of 1kg of a substance by 1 K. Unit is J kg^-1 K^-1.
Specific heat capacity equation
Q = mc🔺ø
1st Law of Thermodynamics
The heat energy supplied to a system either increases the internal energy of the system or enables it to do work
Q = 🔺U + W
Where
Q = net heat input
🔺u = change in internal energy
W = net work output
2nd Law of Thermodynamics
Heat cannot be transferred from one body to a second body at higher temperature.
The entropy of a closed system increases with time.
🔺U = T🔺s - W
Where 🔺U = change in internal energy T = temperature 🔺s = change in entropy W = work done
What is entropy ?
A measure of the unavailability of its energy to do work
What is heat of combustion ?
The heat of combustion is the energy released as heat when a compound undergoes complete combustion with oxygen under standard conditions .
What are heat engines?
Convert heat into work
What is Molar heat capacity at constant volume (Cv)
The heat required to produce a unit rise of temperature in one mole of gas when the volume is kept constant.
Molar heat capacity at constant pressure (Cv)
The heat required to produce a unit rise of temperature in one mole of gas when its pressure remains constant.
What are the three types of expansion process in gases?
Isobaric, Isothermal and Adiabatic.
What is an isobaric gas expansion process?
takes place at a constant pressure.
What is an isothermal gas expansion process ?
Takes places at a constant temperature.
What is an Adiabatic gas expansion process ?
Takes place in a system that is isolated from its surroundings so that heat does not enter or escape.
Most rapid thermodynamic processes are approximately Adiabatic because heat transfer takes time and a rapid process may be completed before much heat has passed through the walls of the system.
How does a refrigerator extract heat?
It’s a heat engine that operates in reverse.
It uses a heat pump to extract heat from a low temperature reservoir and transfer it to a high temperature reservoir. Supplying as much heat as possible to the hot body, further cools the cool body.
What is sensible heat?
Describes an amount of heat when added or removed from a substance causes a change in temperature but not a change in state.
Ideal gas equation
PV = nRT
R = universal gas constant
What is Boyle’s law?
Asserts that if the temperature of a sample of gas is kept constant then the product of its pressure and volume remains constant as the given sample is compressed or expanded.
P1V1 = P2V2
what is Charles law?
Asserts that if the pressure of a gas is kept constant, then the ratio of volume to temperature remains constant as a sample of gas is heated or cooled.
V1 / T1 = V2 / T2
The entropy of a closed system increases with …
time
What is the combined gas law?
A single equation to combine the seperate gas laws .
P1 x V1 / T1 = P2 x V2 = T2.
