Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

University year 1 semester 2 > Mass And Energy Balances > Flashcards

Mass And Energy Balances Flashcards

1
Q

How do you calculate the mol fraction and how is it denoted?

A

Mol fraction = mol of particular substance/total moles present in system.
x - liquid phase mol fraction
y - vapour/gas phase mol fraction
z - mixed system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How do you calculate mass fraction and how is it denoted?

A

Mass fraction = mass of component/total mass in system.

Mass fraction is denoted by w

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do you calculate specific gravity/relative density?

A

Density of substance at stated T and P/density of reference substance at same stated conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is Dalton’s law of partial pressures?

A

The total pressure of a gas equals the sum of pressures exerted by the individual molecules of each component gas were they to occupy the volume of the system at the same temperature as mixture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the partial pressure of a component in a gas mixture?

A

The pressure that component exerts were it isolated in the system volume at the system temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the ideal gas law?

A

PV = nRT

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the equation for calculating partial pressure from mol fraction and total pressure?

A

PA = yA x P

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is Amagat’s law of additive volumes?

A

The total volume of an ideal gas mixture is equal to the sum of volumes of the individual components if they were measured at the same temperature and pressure as the whole mixture.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What can be said about the volume fraction and mol fraction for an ideal gas?

A

They are equivalent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Define a gas.

A

A gas is a vapour phase component that cannot be condensed by isothermal compression.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Define a vapour.

A

A vapour is a gas phase component that can be condensed by isothermal compression.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the saturated vapour pressure?

A

The pressure of a system when the vapour and liquid phases of a component are in equilibrium.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the triple point?

A

The point when liquid, solid and vapour are in equilibrium. This is a unique property of the material, it can’t be predicted, must be measured.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the critical point?

A

The point on a vapour/liquid equilibrium line where the physical properties of the vapour and the liquid phases become the same.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does cooling a gas isobarically mean?

A

Cooling a gas at constant pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is sensible heat?

A

A heat exchange that can be sensed by a temperature change.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is latent heat?

A

An energy change that doesn’t cause a change in temperature but causes a change in phase.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How do you calculate the mol of a substance in mol and kmol?

A

In mol, it’s mass in grams/RMM

In kmol, it’s mass in kg/RMM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

When does a liquid boil?

A

When the system pressure equals SVP

20
Q

What is Raoult’s law?

A

At equilibrium for an ideal system the partial pressure of a vapour phase component equals the SVP of that component at system temperature multiplied by the mol fraction of that component in liquid phase.

21
Q

What is Cv?

A

The specific heat capacity at constant volume, and it’s the energy required to increase the temperature of a unit mass of material by 1 kelvin at constant volume.

22
Q

How can internal energy change be calculated using Cv?

A

du = CvdT so the integral of du equals the integral of CvdT so u2-u1 = integral from T2 to T1 CvdT
Then multiply the change in energy by the number of moles being heated.

23
Q

What is Cp?

A

The specific heat capacity at constant pressure, and it’s the energy required to increase the temperature of a unit mass of material by 1 kelvin at constant pressure.

24
Q

How can the change in enthalpy be calculated from Cp?

A

dh = CpdT so the integral of dh from h2 to h1 equals the integral from T2 to T1 of CpdT
so h2-h1 = the integral from T2 to T1 of CpdT.
Then multiply the change in enthalpy by the number of moles being heated.

25
Q

How do you find the Cp of a mixture?

A

The sum of each components Cp value multiplied by the components mol fraction, if units are on a molar basis (J/mol K) or if units are on a mass basis (J/mol K) then multiply each Cp value by the mass fraction of component.

26
Q

How would you calculate the enthalpy change of a reaction of the form A + B —> C + D?

A

The sum of the enthalpy of formation of the products minus the sum of the enthalpy of formation of the reactants.

27
Q

What is the standard enthalpy change of formation?

A

Enthalpy change when a molecule is made from it’s constituent elements at 298 K and 1 atm.

28
Q

What is Hess’s law of heat summation?

A

The enthalpy change of any reaction may be expressed as the sum of the enthalpy changes of a series of reactions in to which the overall reaction may be formally divided.

29
Q

If a reaction is carried out at above 298 K, how can we determine the change in enthalpy of reaction?

A

Enthalpy received by cooling reactants + change in enthalpy of reaction at 298 K + enthalpy required to heat products from 298 back to reaction temperature. This can also be written as the enthalpy change of reaction at 298 K + the integral from reaction temperature to 298 of (Sum of each components Cp value multiplied by number of moles of component of the products minus the sum of each components Cp value multiplied by number of moles of component of the reactants)dT

30
Q

What’s the equation for the equilibrium constant, Kp, of a reaction of the form
aA + bB —> cC + dD?

A

Kp = (PC^c x PD^d)/(PA^a x PB^b) where PC, PD, PA, and PB are the partial pressure of components and a, b, c, and d are stochiometric coefficients.

31
Q

What is the phase rule used for and what is the equation for it?

A

The phase rule helps you define how many variables the user needs to set to fully define the system, it refers only to a system at equilibrium.
F = C - Ph + 2 where F is the number of degrees of freedom that the user can define to fully specify the system, C is the number of components present in the system, and Ph is the number of phases that can exist, i.e. gas, liquid or solution. All the properties used must be intensive - not depend on quantities of materials present.

32
Q

What is accumulation?

A

Input - output + generation - consumption
It occurs when the inventory of a particular species within system increases or decreases during the time interval under consideration.

33
Q

What is stream flow?

A

Flow of material in the stream (mol/unit time or mass/unit time)

34
Q

How would you calculate the flow of a component into a system?

A

Multiply the total molar flow by the mol fraction of that component. Or multiply the total mass flow by mass fraction.

35
Q

If using molecular balances for reacting systems, how do you calculate the mass flow of an atomic species in a stream?

A

The sum of Wip x P x Fzi

Where Wip is the mass fraction of molecule i in stream P, and Fzi is the fraction of atoms z in molecule i

36
Q

What is recycle and why recycle?

A

It is return of part or whole of process stream to upstream process unit. It’s to save energy or to maximise usage of reactants.

37
Q

What is a bypass?

A

The direction of part or whole of the process stream round rather than through a process unit and the recombination of the streams downstream of the unit.

38
Q

What is purge?

A

The continuous part or complete removal from either a unit or process stream of an undesirable component. The purge consists of the component itself or the component in association with other constituents.

39
Q

What is the gross calorific value?

A

The energy released per unit mass of fuel when any water released appears as liquid.
gross = net + mhfg where m is the mass of water per unit mass of fuel and hfg is the enthalpy of phase change for water at datum conditions.

40
Q

What is the net calorific value?

A

The energy released per unit mass of fuel or per unit volume of gaseous fuel when any water produced appears as water vapour.

41
Q

For combustion, we use excess air. How do we calculate the fraction of excess air?

A

(Actual amount fed - amount for complete combustion)/(amount for complete combustion)

42
Q

What is work?

A

The energy transfer between the system and surroundings due to a vector force acting through a vector displacement.
W = integral of FdL

43
Q

How do you calculate kinetic energy and potential energy?

A 
KE = 0.5mv^2
PE = mgh
44
Q

What is internal energy?

A

Macroscopic measure of the molecular and sub-atomic energy in system - it is not measurable directly. There is no unified zero point.

45
Q

What is heat of solution?

A

Energy change when solvated is dissolved in solvent to form a solution.

University year 1 semester 2 (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions