Thermodynamics process

In summary, the problem involves a thermodynamics process with constant pressure, constant volume, and adiabatic conditions. The goal is to use the equation Q = Cp * n * change in temperature to find the change in temperature. The specific heat at constant pressure, Cp, is known to be 20.8 J/mol*K for an ideal monatomic gas. By using the given pressure and volume values, the change in temperature can be calculated. The final solution is Q = -300 joules, indicating that 300 joules of heat flows out of the gas in going from C to A.
  • #1
blumfeld0
148
0

Homework Statement



i have a thermdyanmics process. with a constant pressure, constant volume and adiabatic. please see the attachment.

Homework Equations



from C->A (constant pressure)
so change in pressure = 0
equations needed to do this problem:


Pressure* V = n *R* T -----------> main equation
heat = Q = Cp * n * change in temperature ----------------> main
(Cp is called the specific heat at constant pressure)

The Attempt at a Solution



our goal is use Q = Cp n * change in temperature

BUT we don't know change in temperature
we know Cp = 20.8 for an ideal monatomic gas (just a constant you look up in a physics textbook)
n = 1 mole

so how do we find change in temperature?

we need to use P Vinitial = n R Tinitial
400 * (1) = 1 * 8.315 * Tinitial

so Tinitial = 48.1058 Kelvin

P Vfinal = n R Tfinal

400 * 2 = 1 * 8.315 * Tfinal
so Tfinal = 96.2117 Kelvin

now we are done!

Q = n * Cp * change in temperature

Q = (1) *( 20.8 J/mol*K ) (96.2117 - 48.1058 Kelvin)
Q = 1000.6 Joules


is this right?

thank you
 

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  • #2
This is just a first law problem: dQ = dU + dW where dW is the work done by the gas. For C to A:

(1) [tex]\Delta Q_{CA} = \Delta U_{CA} + W_{CA} = \Delta U_{CA} + P\Delta V_{CA}[/tex]

You know that the change internal energy from C to A is +100 J (to balance the 200 J loss from A to B and 100 J gain from B to C).

You can also determine the work done from C to A because you are given the pressure and change in volume.

So plug those values in (1) to give you [itex]\Delta Q_{CA}[/itex]

AM
 
  • #3
thank you!
why was i off? i thought i had this!


so Q = U + W
Q = 100 + (400pascals * (2-1)m^3)
Q= 500 joules?

or is it

Q = 100 - (400pascals * (2-1)m^3)
Q= -300 joules.

which one is right?

thank you!
 
  • #4
blumfeld0 said:
thank you!
why was i off? i thought i had this!


so Q = U + W
Q = 100 + (400pascals * (2-1)m^3)
Q= 500 joules?

or is it

Q = 100 - (400pascals * (2-1)m^3)
Q= -300 joules.

which one is right?

thank you!

Heat flow out of the gas is negative. Heat flow into the gas is positive. Work done by the gas is positive. Work done on the gas is negative.

So:

[tex]\Delta Q = \Delta U + P\Delta V = +100 + 400 * (-1) = -300 J[/tex]

This means that 300 J of heat flows out of the gas in going from C to A.

AM
 

1. What is thermodynamics process?

Thermodynamics process is the study of the relationship between heat, work, and energy in a system. It explains how energy is transferred and transformed during physical and chemical changes.

2. What are the laws of thermodynamics?

The laws of thermodynamics are fundamental principles that govern energy and its transformations in a system. The first law states that energy cannot be created or destroyed, only transferred or converted. The second law states that the total entropy of a closed system will always increase over time. The third law states that the entropy of a pure crystalline substance at absolute zero temperature is zero.

3. How is thermodynamics related to chemistry?

Thermodynamics is closely related to chemistry because it explains how energy is involved in chemical reactions. It helps us understand the energy changes that occur during a chemical reaction and how to predict the direction of a reaction.

4. What are the different types of thermodynamic processes?

There are four main types of thermodynamic processes: isothermal, adiabatic, isobaric, and isochoric. An isothermal process occurs at a constant temperature, an adiabatic process occurs without the transfer of heat, an isobaric process occurs at constant pressure, and an isochoric process occurs at constant volume.

5. How is thermodynamics used in engineering?

Thermodynamics is crucial in engineering as it helps engineers design and optimize systems that involve energy transfer. It is used to calculate the efficiency of engines, turbines, and other machines, as well as to design refrigeration and heating systems. It also plays a vital role in the development of new materials and technologies.

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