First Law of Thermodynamics

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First Law of Thermodynamics. Contributions by: John L. Falconer &amp; Will Medlin Department of Chemical and Biological Engineering University of Colorado Boulder, CO 80309-0424 Supported by the National Science Foundation.

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### First Law of Thermodynamics

Contributions by:

John L. Falconer & Will MedlinDepartment of Chemical and Biological EngineeringUniversity of ColoradoBoulder, CO 80309-0424

Supported by the National Science Foundation

An unknown compound is at 200°C and 1 MPa. How many phases could be present?

1

2

1 or 2

3

Not possible to specify both temperature and pressure

A mixture of ethanol and propanol are at 60°C. Both liquid and vapor are present. How many additional variables can be specified before the system is completely determined?

0

1

2

3

A mixture of ethanol and propanol are at 60°C. Both liquid and vapor are present. The pressure is 1 bar. How many additional variables can be specified before the system is completely determined?

0

1

2

3

A mixture of ethanol and propanol are at 60°C. Both liquid and vapor are present. The pressure is 1 bar and the liquid mole fraction of ethanol is 0.5. How many additional variables can be specified before the system is completely determined?

0

1

2

3

Which of the following is not possible:

2 components in VLE equilibrium, both temperature and pressure are specified.

1 component in three phases: solid, liquid, gas.

2 solids in equilibrium at a specified temperature.

2 components as solid and liquid, with temperature, pressure, and mole fractions specified.

1 component as a gas, temperature and mole fractions specified.

When a hydrogen molecule dissociates into two H atoms, energy is ______________.

removed

H

H

H

H

Insulation

System

Consider a completely insulated, closed system of fixed volume. The exothermic thermite reaction takes place in the system. The system energy __________.

increases

decreases

stays the same

Insulation

Container

An endothermic reaction takes place in a completely insulated, closed container of fixed volume.

The internal energy of the container _____________.

increases

decreases

stays the same

An endothermic reaction takes place in an isothermal, closed container of fixed volume.

The internal energy of the container ____________.

increases

decreases

stays the same

An exothermic reaction takes place in an isothermal, closed container of fixed volume. The internal energy of the container _____________.

increases

decreases

stays the same

An endothermic reaction takes place in a continuous-flow, isothermal reactor at constant pressure.

The enthalpy of the effluent is _________________ the enthalpy of the inlet.

higher than

lower than

the same as

An exothermic reaction takes place in a continuous-flow, isothermal reactor at constant pressure.

The enthalpy of the effluent is ____________ the enthalpy of the inlet.

higher than

lower than

the same as

An endothermic reaction takes place in a continuous-flow, adiabatic reactor. The enthalpy of the effluent is ____________ the enthalpy of the inlet.

higher than

lower than

the same as

An exothermic reaction takes place in a continuous-flow, adiabatic reactor. The enthalpy of the effluent is _____________ the enthalpy of the inlet.

higher than

lower than

the same as

A weight hangs by a thin thread from a black box that is completely isolated from the surroundings. The weight slowly rises.

The energy of the box ___________.

increases

decreases

does not change

BLACK

BOX

TABLE

Very thin

Weight slowly drawn up to box

Two adiabatic reactor setups contain the same reaction with 70% conversion at steady state. The preheater heats the feed stream and causes a 200°C decrease in the reactor effluent. Assume perfect heat exchangers. The exit temperature of the system with the preheater is ______________.

500°C

600°C

700°C

100oC

500oC

X=0.7

Reactor

T = ?

X=0.7

100oC

Reactor

Pre-Heater

A steady state, adiabatic reactor is fed a mixture of A and an inert; the flow rate of each is 10 mol/hr. The exothermic reaction A  B goes to completion. The outlet temperature is 400oC. When the flow rate of A is increased to 20 mol/hr while the inert remains at 10 mol/hr, conversion is still complete and the effluent temperature _____________.

increases

decreases

remains the same

X = 1.0

T = 400oC

10 mol/hr

A

A  B

Inert

10 mol/hr

X = 1.0

T = ?

20 mol/hr

A

A  B

Inert

10 mol/hr

An endothermic reaction (A  C) takes place in an adiabatic flow reactor. The feed is a 50/50 mixture of reactant A and inert B. At a flow rate of 10 mol/hr, conversion of A is 100% and the outlet temperature is 60oC. The feed flow rate is doubled, and only 75% of A is converted to C. The outlet temperature is _____________ 60oC.

higher than

lower than

equal to

X = 1.0

T = 60oC

10 mol/hr

A

B

A  C

X = 0.75

T = ?

20 mol/hr

A

B

A  C

gas flow

-PDV

-D(PV)

-VDP

None of the above

What is the equation for work for steady-state flow?

An ideal gas goes from state 1 to 2 by two processes. Process A is reversible and has 50 kJ of work done on the gas. Process B is irreversible and has 200 kJ of work done on the gas. If one process requires heat to be added and the other removed, which process has to have heat added?

Process A

Process B

50 kJ

1

2

200 kJ

1

2

A gas undergoes reversible expansion from 40 barand 500 K to 5 bar and 500 K by two pathways.

Which process creates more |work|?

A constant pressure process to the final volume and then constant volume to 5 bar.

A constant volume process to 5 bar and then constant pressure to the final volume.

Same work for both

Methane at 15 bar and 120°C flows into an evacuated container when the valve is open. When the pressure in the container reaches 15 bar, the temperature of the methane is _______ 120°C.

greater than

less than

equal to

CH4

120°C

15 bar

Container

Methane at 15 bar and 120°C flows into a container that has methane at 120°C and 2 bar when the valve is opened. When the pressure in the container reaches 15 bar, the temperature of the methane in the container is ___________ 120°C.

greater than

less than

equal to

CH4

CH4

120°C & 2 bar

120°C

15 bar

1  2  3  1

1  4  5  1

Both have the same Q

Q is zero for both pathways

An electric fan is turned on in a room with all the doors closed. The room temperature ___________.

increases

decreases

remains the same

A battery-operated fan is turned on in a room with all the doors closed. The room temperature ______________.

increases

decreases

remains the same

A battery-operated fan is turned on in a room with all the doors closed. The energy in the room ______________.

increases

decreases

remains the same

A refrigerator door is opened in a kitchen and all the doors to the kitchen are closed. The kitchen temperature ______________.

increases

decreases

remains the same

An ideal gas is compressed to 10 times its initial pressure. The final volume is smaller for _________.

an isothermal compression

neither. It is the same in both.

Which substance at 25°C requires the most work per kg to compress from 1 bar to 25 bar?

Water

Hexane

Mercury

Air

Same work for all

Which of the following, when fed with an organic to an oxidation reaction, has the higher adiabatic temperature?

A stoichiometric amount of pure O2

50% excess oxygen (pure)

A stoichiometric amount of air

One kg of steam

One kg of liquid water

Both systems have the same internal energy

A pot of water is boiling open to the atmosphere when the pot is sealed by a tight lid, and continued heating causes the pressure to rise. Compared to before the lid was added, the temperature _____________.

increases

remains the same

decreases

H2O

Air is contained in a sealed tank of fixed volume. The air in the tank is initially at 20°C and 1 atm. It is then heated to 250°C. The energy of the air in the container ___________.

increases

decreases

does not change

Gas

250°C

Gas

20°C

1 atm

Start

After heating