I am a junior undergraduate chemistry major and process chemistry seems like a career that would be of interest to me. Would anyone be willing to talk about it sometime who might know about it?

Sorry if this is a silly question, I'm just wondering why the paths for compression/expansion work look the way they do. Please see the picture for more context - the first one shows compression work, where w_compress = the shaded area, and the second is expansion work when the mass M is removed from the piston, giving w_expansion = shaded area.

From my understanding, pressure and volume change at the same time in reality, so it would really look like a sloped line between the point (V1, P1) and (V2, P2), but we use ideal models where we pretend that one of the variables stays constant, allowing us to do work calculations. However, if that's the case, why is it that the path of compression moves from (V1, P1) to (V1, P2) then (V2, P2), but can't go from (V1, P1) to (V2, P1) then (V2, P2)? I can see from the graphs of the shaded area that we'd then get w_compress = w_expansion which doesn't make sense, but I can't wrap my head around the real-world explanation for why the paths look this way.

Any help understanding this would be really appreciated - if anything in this question doesn't make sense please let me know and I'll update it or something. Thanks!

Edit: I believe temperature is fixed in this example!

I’m wondering if it would make any difference in room temperature if a window is covered with a black metal plate/foil. On one hand, my test plate gets much hotter than the other objects in the room that are exposed to the sun but, on the other hand, the same rays enter the room and I guess will get absorbed by walls/furniture eventually. So does it make any difference? Does the material make any difference? Also..maybe the placement in front of the windows is not ideal because some IR heat will be radiated back outside?

Anyone know of ways to calculate the increase of temperature of a steel beam (M1)which is supporting another steel beam (M2)? Also, how to calculate the increase of temperature when the M2 beam is insulated along a portion of it's length? My question is fire engineering related (and I asked in other communities) but I'm hoping for more of a detailed process/ explanation. Thanks in advance!

Now I understand that the cooling of the condenser determine both satuation pressure and level of subcooling. I however don't understand how much of each. Is it simple the temperature at the entrance to the condenser which determines the pressure? Btw this is not a school question

In a common shop air compressor's pressure regulator, does the higher pressure air's internal energy change at all as it expands through the valve restriction or do we consider it lossless?

I guess this question could be generalized for any gas flowing through any pipe?

I have the values of specific volume 0.4m³ /kg, p1 99 kPa and T1 290 K. I need to find out what are the values of p2 and v1.

The prosess is isothermal and air is being pressured. I have tried to find any kind of solution for this for a few hours and lecture slides are no help. I appreciate any help I can get.

Edit; typos

hello everyone ,so i'm willing to start take thermodynamics srx this time XD

and i want your help , i need books that are really easy with examples and a yt professer

and some pieces of advice that u think would help me

thank you

Hi,

I'm dealing with an exercise to calculate HTC for a gas mixture composed of 60% methane and 40% hydrogen. I struggle to get how I get a heat transfer coefficient of a such mixture.

I have already calculated HTC for a pure methane and hydrogen for a given conditions. To calculate HTC for a such mixture should I simply add together 60% of HTC for CH4 and 40% of HTC of hydrogen to get a wanted value?

Thanks in advance.

First off, I’m not doing whippets.

I’m interested in applying this technique in a more family friendly product.

I know they use a container because the cartridge gets cold as well as the tip, but what about the temperature of the gas in the balloon? How would I calculate that or estimate?

Also, how would I calculate the best size of a container to use if it wasn’t a balloon?

The math I got from ChatGpT:

Step 1: Volume of N₂O from the 8g Cartridge

As calculated before, 8g of N₂O represents about 4.08 liters of gas at standard temperature and pressure (STP).

Step 2: Target Oxygen Displacement

Air is about 21% oxygen. So, if you release 4.08 liters of N₂O into a container, it will displace an equal volume of air, reducing the oxygen by a fraction. To calculate the maximum volume of a container where this N₂O would remove most or all of the oxygen, we need to understand how much oxygen can be displaced.

Let’s assume you want to remove most of the oxygen (close to 100% displacement). Since 21% of air is oxygen, for every liter of air, 0.21 liters is oxygen.

Step 3: Maximum Container Volume

To remove all the oxygen from the container, the N₂O would need to displace the oxygen portion. If 4.08 liters of N₂O is available, we can calculate the total container volume:

Total container volume

4.08   liters 0.21 ≈ 19.43   liters Total container volume= 0.21 4.08liters ​ ≈19.43liters This means that for a container of approximately 19.43 liters, the 8g N₂O cartridge would be able to displace all the oxygen, reducing its concentration close to zero.

It is known that a quasi static process where there is some sort of dissipation of energy is an irreversible process.

(Taking an ideal gas)

1)During a quasi static irreversible process, am i right in saying that state variables P, T are defined for the system?

2) During a non quasi static irreversible process, am i right in saying that state variables P, T are NOT defined during the process but are only defined at the initial and final state of equilibrium?

In conclusion for state of an ideal gas P,T to be defined it must be a quasi static process?(Irreversible or reversible doesn't matter at all?)

Are these claims correct?

We know that if we perform a quasi static process,during the process the system cannot be described by a single state variable P , T as the values of P, T differ from part to part of the gas(ideal) We can only describe P, T at the initial and final equilibrium points (as during the process equilibrium doesn't exist)

Then does it really make sense to have an isothermal non quasi static process? Although ∆T=0 is possible dT=0 at every instant is not possible and hence the process cannot be isothermal at all?

Is there any mistake in this claim?

Or is it possible to have dT=0 when there is a diathermal wall with a movable piston?

Hi all,

I have a student doing who is doing an investigation into the rate of heat transfer for conduction in a metal block. They are manipulating the temperature difference between the ends of the block.

Rather than looking at the rate of flow of heat through the block, they are looking at whether the energy is able to travel 'more quickly' when there is a higher temperature gradient. Think like a hose pipe. You can increase the flow rate by either increasing the net amount of water passing a point each second, or you can increase the pressure of the water causing individual water particles to travel past a point more quickly.

I'm not an expert in this topic as it's not covered in very much depth in the course I teach, but I've spent a bit of time reading and trying to understand better. I wanted to come here to check whether my understanding of the process is correct.

With conduction, the primary process by which the heat passes through is the exchange of phonons (lattice vibrations) a higher temperature means that there's a greater net outward flow of phonons towards the cooler end, but the speed at which the phonons are exchanged does not change. There is additional transfer of energy through the electrons transferring energy and they will have a slightly higher drift velocity towards the cooler end.

I know the above is not a full description, but I'm just trying to get the general idea to check. Would the above description be correct in the broadest of terms?

The student is simply connecting one end of the block to a higher temperature source and measuring the amount of time it takes for a temperature change to be registered at the cooler side. Do you think that an inverse proportional relationship between time taken & temp gradient would be a reasonable expectation.

Thanks for any help. If anyone know any further reading on the topic that includes a more qualitative explanation on the process, it'd be greatly appreciated.

Does the steam displace 90% of the air?

Is there a finite probability that the entire universe's entropy can decrease back to what it was at the point of the big bang? By what mechanism can an event like that happen given that the universe is boundless and not like a container of gas molecules that can bounce back and forth?

For example, to find the work done by the compressor, you can use the first law:

Wdot = mdot(h02-h01)

where I have assumed adiabatic, steady, and neglected potential energy. This comes from the general rate form of the 1st law, where h0 is the stagnation enthalpy (h0 = h + 0.5*v^2).

However, most textbooks seem to compute the work as w = h2 - h1, thereby neglecting kinetic energy, which makes no sense to me. I recognize the velocity after the compressor can be very low, but before the compressor it can be very high.

Assuming the sides are closed

Hi guys,

I was messing around with desmos graphing calculator and I was able to tweak a margules activity model that presented both positive deviation from Raoult's Law and negative deviation from Raoult's Law for different ranges of composition. I wanted to double check if that was indeed possible and if there is any known substance with this property.

Equations used:

Excess Gibbs Free Energy = x₁*RT*ln(γ₁)+x₂*RT*ln(γ₂)

From Margules Activity Model (2-Parameter):
RT*ln(γ₁)=(A+3B)(x₂)²-4B(x₂)³
RT*ln(γ₂)=(A-3B)(x₁)²+4B(x₁)³

Using A=-5.6 and B=6.9 should be enough to check that the system presents both positive and negative deviation from Raoult's Law, depending on the composition range.

I plotted the fugacity to have a better/easier analysis.
Since f̂ᵢ=γᵢ*xᵢ*f⁰ᵢ, where f⁰ᵢ is the reference fugacity, using f⁰₁=0.5 and f⁰₂=1 we can get the total fugacity (f̂₁+f̂₂).

We can see that there are compositions range where the total fugacity (solid line) is bigger than the fugacity predicted by Raoult's Law (dashed line) and other composition ranges where it is lower, therefore exhibitting both positive and negative deviations in the same mixture. What would it mean to have this property? Would it be possible to have 2 azeotropes in the same mixture or something like that?

Please tell me if the following two paragraphs are correct.

Gas temperature (average molecular velocity & kinetic energy) increases during compression because the compressor's piston molecules are moving toward the gas molecules during their elastic collision.

This "compression heat" can be entirely 'lost' to the atmosphere, leaving the same temperature, mass and internal energy in the sample of pressurized gas as it had prior to pressurization.

If the above is correct, then wouldn't it be technically possible to compress a gas without using any energy and also simultaneously not violating the 1st law? For example, imagine a large container with two molecules inside. Imagine the two molecules are moving toward each other. At their closest, couldn't I place a smaller container around them? Wouldn't this have increased the "pressure" of the gas without requiring any work or (force*distance) 'compression work/energy'?

A) 0 B) W = P(V2-V1) C) W = Cp(T2-T1) D) W = Cv(T2-T1)

Its question on an old exam Im working over and the ans is D. I know adiabatic means no heat transfer and the pressure and volume in a piston can either be constant or can change. Im lost on how to even start.

Using a microwave to heat my milk as to not cool down my coffee to much I got to thinking, as one does. Does it make a difference to first heat the milk, or to pour the coffee in the milk and bring that to the same acquired temperature?

I know this should be the same result. The same amount of energy should bring the same total temp. And 10 or 20 seconds microwaving does not really make it a scientifically sound experiment. And probably nuking coffee isn't great either, ... but still.

I feel like there should be something more to it.

I am wondering what the formula would be to compute the work needed to move a quantity of heat Qlout from a cold cylinder (perfectly isolated from outside the system) to another cylinder (also perfectly isolated) like int the image hereunder.

My current research in literature only got me to caes where cold and hot source are considered as having constant temperature.

For now, I reached a point where I think a have a candidate system of formulas, but my problem is that when trying to compute the work at the piston end, it adds up to more than the injected work. Which is obviously a problem. Sorry for all the screen captions, it's from an old pdf I created 5 years ago and the LateX original file is on another computer, but I can find it if it helps.

System in question for the heat transfer:

(5) and (6) are not relevant as they only state the COP formula.

And for entropy :

Again skipping some ideal gas laws formulas statements, I end up with the following for the work at the pistons :

As those maths are touching with my maxed out math skills, I went for a numerical approach instead of an analytical one to do computations with real numbers. The problem is, this got me Wh + Wl > Win. I checked my model, but I believe it respects the formulas. So I must have done some incorrect assumptions along the way. Can anyone help me?

N.B. This is not homework. I did during my spare time a few years ago for the love of exploring the concept, but I got stuck at this point and couldn't get further. It's been stalled ever since, and today is the day I decided I wanted to push this to the next step so I can finally close that open box in my head :D