Mid term chapter 2 Flashcards
For a substance, what is the difference between mass and molar mass? How are these two related?
Mass m is the actual mass in grams or kilograms molar mass is the mass per mole in grams per mole or kilograms per kilomole these two are related to each other by m= NM. Where N is the number of mols
What is the difference between intensive and extensive properties?
Intensive properties do not depend on the size extent of the system, but extensive properties do depend on the size extent of the system
What is specific gravity? How is it related to density?
Specific gravity or relative density is defined as the ratio of the density of a substance to the density of some standard substance add a specified temperature which is the density of water at 4°C or 1000 kg/m³ specific gravity is known density can be determined
The specific weight of system is defined as the weight per unit volume is the specific weight and extensive or intensive property?
Specific weight is an intensive property. As y = W/V if we were to divide the system into 2/2, each half weighing W divided by two and occupying a volume of V/2 the specific weight of one of these halves is y = W/2/V/2. Which is exactly the same as the original equation. Afford to be an extensive property value for half of the system would be halved
What is the state postulate?
The state postulate is expressed as: the state of a simple compressible system and completely specified by two independent intensive properties
Under what conditions is the ideal gas assumption suitable for real gases?
A gas can be treated as an ideal gas when it is at a high temperature and or a low pressure relative to its critical temperature and pressure.
What is the difference between R and Ru? How are these two related?
Ru is the universal gas constant that is the same for all gases, where is R is the specific gas constant that is different for different gases. These two are related to each other by. R= Ru/M where is the molar mass
What is cavitation? What causes it?
In the flow of a liquid, cavitation is the vaporization that may occur at locations where the pressure drop below the vapor pressure. The vapor bubbles collapse as they are swept away from the low pressure regions, generating highly destructive extreme high pressure waves. This phenomenon is common, cause for drop and performance and even erosion of impeller blades.
Does water boil at high temperatures at higher pressures?
Yes. The saturation temperature of pure substance depends on pressure. In fact it increases with pressure. The higher, the pressure, the higher, the saturation or boiling temperature.
If the pressure of a substance is increased during a boiling process, will the temperature also increase or will it remain constant? Why?
If the pressure of a substance increases during a bowling process, the temperature will increase since the boiling or saturation temperature of a pure substance depends on pressure and increases with it
What is vapor pressure? How is it related to saturation pressure?
Vapor pressure Pv of a pure substance is defined as the pressure exerted by a vapor in phase equilibrium with its liquid at a given temperature. In general, the pressure of a vapor or gas, whether it exists alone or in a mixture with other gases is called the partial pressure. During face change processes between the liquid and vapor phase of a pure substance, the saturation pressure and the vapor pressure are equivalent sensitive vapor is pure..
What is flow energy? Do fluids at rest possess any flow energy?
Flow energy or flow work is the energy needed to push fluid into or out of control. Fluids at rest do not possess any flow energy.
How do energies of a flowing fluid and a fluid at rest compare? Name the specific forms of energy associated with each case
A flowing fluid possesses flow energy, which is the energy needed to push a fluid into or out of a control volume, in addition to the forms of energy possessed by a non-flowing fluid the total energy of non-flowing fluid consist of internal and potential energy. If the fluid is moving as a rigid body, but not flowing, it may also have kinetic energy. The total energy of flowing fluid consists of internal kinetic potential and flow energies.
What is the difference between macroscopic and microscopic forms of energy?
Microscopic forms of energy are those a system possesses as a whole with respect to some outside reference frame. The microscopic forms of energy on the other hand, are those related to the molecular structure of the system and the degree of the molecular activity and our independent of outside reference frames.
What is total energy? Identify the different forms of energy that constitute the total energy.
The sum of all forms of energy a system possesses are called total energy. In the absence of magnet, electrical and surface tension effects, the total energy of a system consists of the kinetic, potential, and internal energies.
List the forms of energy that contributes to the internal energy of a system
The internal energy of a system is made up of sensible, latent, chemical, and nuclear energies. A sensible internal energy is due to transitional rotational and vibrational effects.
How are heat, internal energy, energy and thermal energy related to each each other?
Thermal energy is the sensible and latent forms of internal energy. It does not include chemical or nuclear forms of energy in common terminology. Thermal is referred to as heat however, like work heat is not a property where is thermal energy is a property.
Use average specific heat explain how internal energy changes of ideal gases and incompressible substances can be determined
Using specific heat values at the average temperature, the change in specific internal energy of ideal gases can be determined from delta u = c_vavg delta T. For incompressible substances cp= cv = c and delta u = c_avg delta T.
Using average specific, explain how an enthalpy changes of ideal gases and incompressible substances can be determined
Using specific heat values at the average temperature, the change in specific anthropopathy of ideal gases can be determined from delta h = c_pavg deta T. For incompressible substances. C_p = C_v =c and delta H = Delta u + v DeltaP
What does the coefficient of compressibility of a fluid represent? How does it differ from isothermal compressibility?
Coefficient of compressibility represents the variation of pressure of a fluid with volume or density at constant temperature. I saw the milk compressibility is the inverse of the coefficient of compressibility and it represents the fractional change in volume or density corresponding to a change in pressure.
What does the coefficient of volume expansion of a fluid represent? How does it differ from the coefficient of compressibility?
The coefficient of expansion represents the variation of the density of a fluid with constant pressure. It differs from the coefficient of compressibility, and not the latter represents the variation of pressure of fluid with density at constant temperature.
Can the coefficient of compressibility of a fluid be negative? How about the coefficient of volume expansion?
The compressibility of a fluid coefficient of compressibility of fluid cannot be negative, but the coefficient of volume expansion can be negative
What is viscosity? What is the cause of it in liquids and in gases? Do liquids or gases have higher dynamic viscosity?
Viscosity is a measure of the stickiness or resistance to deformation of fluid. It is due to the internal frictional force that develops between different layers of fluids as there forced to move relative to each other. Viscosi is caused by cohesive forces between the molecules and liquids and buy the molecular collision and gases. In general liquids have higher dynamic causes and gases.
What is a Newtonian fluid? Is water a Newtonian fluid
Fluids stress is proportional to the velocity gradient are called Newtonian fluids. Most common fluid such as water gasoline and oils are newton and fluids.
How does the kinetic viscosity of a liquid and gas vary with temperature?
For liquids, the kinetic viscosity decreases with temperature for gases. The kinetic viscosity increases the temperature.
How does the dynamic viscosity of a liquid and gas vary with temperature?
The dynamic viscosity of a liquid decreases with temperature. The dynamic viscosity of gas increases with temperature.
Consider two identical, small glass balls dropped into two identical containers, one filled with water and the other with oil which will reach the bottom of the container first? Why?
When two identical, small balls are drops into two identical containers the one filled with water and the other oil, the ball dropped in the water will reach the bottom of the container first because of the much lower viscosity of water relative to oil
What is surface tension come what causes it? Why is the surface tension also called surface energy
The magnitude of the pulling force at the surface of a liquid per unit length is called surface tension. It is caused by the attract of forces between the molecules. The surface tension is also surface energy since it represents the stretching work that needs to be done to increase the surface area of the liquid by a unit amount.
A small diameter tube is inserted into a liquid whose contact angle is 110°. Will the level of the liquid in the tube be higher or lower than the level of the rest of of the liquid?
The liquid level in the tube will drop the contact angle is greater than 90° and cosine of 110° is less than zero
What is the capillary effect? What causes it? How is it affected by the contact angle?
The capillary effect is the rise or follow the liquid in a small diameter tube inserted into the liquid. It is caused by the net effect of the cohesive forces the forces between like molecules like water and adhesive forces the forces between unlike molecules like water and glass. The capillary effect is proportional to the cosine of the contact angle, which is the angle that the tangent to the liquid surface makes with the solid surface at the point of contact.
Consider a soap bubble. Is the pressure inside the bubble higher or lower than the pressure outside?
The pressure inside is soap. Bowl is greater than the pressure outside as evidenced by the stretch of the soap film.
Is the capillary rise, greater and small or large diameter tubes?
The capillary rises inversely proportional to the diameter of the tube less capillary rises greater in the smaller diameter tube
