Internal energy Definition and 369 Threads

We know that internal energy of ideal gas depends only on temperature. Let's say we have 1 mole of ideal gas with pressure P1, volume V1 and temperature T. Let's call this the state 1. Equation of state for ideal gas applies: PV=RT. Now if we expand (or compress gas) isothermally, gas will then...

Homework Statement A gas bottle contains exactly 158 moles of carbon dioxide CO2. Find the change in the internal energy of this much CO2 when it is cooled from 36C down to exactly 25C at a constant pressure of 1 atm. The gas can be treated as an ideal gas with γ=1.289. The gas constant reads...

I'm struggling to understand a concept which I assume is basic, but I can't seem to fit the pieces together. When speaking about an ideal gas, I understand that ΔH = ΔU + Δ(PV) = ΔU + RΔT So far so good. I also understand the relationship: ΔU = Q + W... (W here is work being done on the...

Homework Statement A pressure cooker is a nearly air tight sealed system. When seated on a stove burner and heated, water turns to steam and increases the pressure inside, resulting in higher temperatures so food cooks faster. Suppose 1/2 cup of water is inside the pressure cooker and it is on...

Homework Statement A 1 m3 rigid tank has propane at 100 kPa and 300 K. The tank is connected to another 0.5 m3rigid tank which has propane at 250 kPa and 400 K by a ball valve. The valve is opened and both tanks come to a uniform state at 325 K. Calculate the change in internal energy and...

Homework Statement 10g of water at 0˚C added to 100g water at 50˚C Homework Equations Qhot+Qcold=0 Q=mcΔT Q=mL Σmc(Tf-Ti)=0 The Attempt at a Solution So I understand this problem, but I'm not sure when I am supposed to use Q=mL, L being the latency, I think. So with the problem mentioned you...

This is my first time here. Sorry if the formatting is a bit off. This is one of a few questions I am having difficulty with. I am not asking for any answers; and I have definitely done the work - multiple times - but have not been able to find the correct answer. Q) A uranium-238 atom can...

In my chemical thermodynamics class/notes (and other references I've used) it is stated throughout that internal energy U is a function of entropy and volume , i.e. it's "natural" variables are S and V: U = U(S,V) I suspect that I must take this "axiomatically" and move on. Since U is a state...

1. Homework Statement When volume changes from V to 2V at constant pressure then the change in internal enrgy will be? 2. Homework Equations ΔU= nCvΔT 3. The Attempt at a Solution I have used the equation ΔU= nCvΔT but the answer is PV/γ-1

Hello Physics Forums! I am currently writing a computer program that displays an enthalpy-pressure diagram for the refrigerant 134a. I am using the data and relation between specific volume, pressure and temperature found in http://eng.sut.ac.th/me/2014/document/LabMechanical1/HFC-134a_SI.pdf...

Hello, Internal energy can be defined theoretically for one molecule (U = 1/2 Kb T) for example but entropy is defined for a system thus for many molecules. Then we define temperature equal to δU / δS but here U can be defined for one molecule, so S can also be defined for one molecule? How...

Homework Statement What is the internal energy of an electron moving at 0.750c0 in the Earth reference frame? Homework EquationsThe Attempt at a Solution E = mc^2 E = (9.11 * 10^-31)(.750)(3*10^8) However, this appears incorrect. What have I done wrong or what am i missing?

Homework Statement One litre cylinder contains 1 mole of the ideal gas molecules having the average kinetic energy of 0.1eV. What is the total energy of this gas? Homework Equations W = K + U The Attempt at a Solution I figured because the cylinder is closed, no stated temperature change, or...

An ideal gas is compressed from a volume of Vi = 4.50 L to a volume of Vf = 3.00 L while in thermal contact with a heat reservoir at T = 295 K as in the figure below. During the compression process, the piston moves down a distance of d = 0.120 m under the action of an average external force of...

Homework Statement Assuming water to be an ideal gas, enthalpy of vaporization is x joules per mole. I have to find change in internal energy an 100 degree Celsius for one mole of water. also find heat absorbed. Homework EquationsThe Attempt at a Solution I initially thought that during...

I've read back and forth in my chapter and tried consulting with my forumla sheet, but I cannot seem to find the correct formula. I bet I am looking at this question wrong, but I am fairly sure I need to use the -100 kJ for something to find the final volume and pressure , along with the given...

Homework Statement Hvap = 22.6E5 J/Kg. R=8.315E3 Jkmol^-1K^-1. 1kmol water = 18kg Keeping in mind that latent heats are enthalpies, what is the change in internal energy when 1kg water is converted to steam at pressure of 1atm and temperature of 100C. Homework Equations dU = dQ - PdV. The...

Hi, I know that changes in entropy can be expressed as a function of temperature, specific volume, and pressure using the fundamental equations of thermodynamics: ds = du/T+pdv/T, where the changes in entropy can be caused by either changing the specific volume or the internal energy. I also...

Homework Statement Show that the internal energy at constant entropy and volume decrease for a spontaneous process Homework Equations F = U-TS The Attempt at a Solution Use Clausius: dS-dQ/dT > 0 Assume constant volume: TdS > dU assume constant entropy this becomes 0>dU Since dU is...

Homework Statement Is it possible to calculate the work done heat transfer, and efficiency of an object in a thermodynamic system, given the Temperature vs Entropy graph? Example: Homework Equations ∆U=Q-W ∆S=dQ/T e=1-(Qc/Qh) e=W/QhThe Attempt at a Solution Since this is a T vs S diagram,i...

Why temparature is only dependent on internal energy of something, say an ideal gas.

Thermodynamics question: Why does the internal energy have a lower bound? I tried to explain it using postulates, but cannot get the connection between the postulates. Please do explain it briefly. Thank you.

Hi, I am having a hard time answering this question. Any help will be appreciated. In 1938, the journal Nature published a paper by R. Emden titled “Why do we have winter heating?” (Nature Vol 141 pp. 908-9 – although you do not need to read it to answer the problem). This article asserts that...

Homework Statement [/B] Homework Equations Assumptions[/B]: Closed System and Quasi-static. p = 90 + 73,386*V -> V = (p-90)/(73,386) v = V/m Q - W = U2 - U1 mass balance: m = m1 = m2 The Attempt at a Solution At state 1: p1 = 110 kPa V1 = (110-90)/(73,386) = 2.725*10-4 m3 v1 = V1/m1...

A system is in contact with a reservoir at a specific temperature. The macrostate of the system is specified by the triple (N,V,T) viz., particle number, volume and temperature. The canonical ensemble can be used to analyze the situation. In the canonical ensemble, the system can exchange...

Homework Statement In a sample of wet steam at 11 bar, 75% of the total internal energy is contained in the vapour portion. Calculate the dryness fraction of the steam to 3 decimal places. Homework Equations u(kJ/kg) = (1-x)uf + x*ug x - dryness fraction f - saturated liquid state g -...

Homework Statement A sample of an ideal gas goes through the process shown in Figure P20.32. From A to B, the process is adiabatic; from B to C, it is isobaric with 100 kJ of energy entering the system by heat. From C to D, the process is isothermal; from D to A, it is isobaric with 150 kJ of...

How is internal energy affected as cold water in a kettle transforms into hot water? [Mentor's note: edited to fix the formatting]

A box is initially at rest on a frictionless surface. David then pushes it and the box moves across the frictionless surface. Let's discuss this process in the context of thermodynamics, especially the First Law. One way to state it is: ΔU=Q−W (where positive W is work done by the system...

For a given closed system that does not experience phase transitions, does its internal energy depend only on its temperature?

ΔU=q-w and in a free expansion w=0 and Free expansion is an irreversible process in which a gas expands into an insulated evacuated chamber. Does this mean that free expansion is an isolated system? Meaning the walls of the container are adiabatic in which no heat can enter the system and so q=0...

Homework Statement A car rubber has the volume 50 liters when it is bloated in a pressur 1.8 atm and in a temperature 293 K. After some hours of journey as an effect of friction the pressure will become 2atm. Find the change of internal energy of the air inside the rubber (U) Homework...

Homework Statement dX = U/V dV + U/p dp Write the differential of X in terms of the independent variables.Prove that this is an exact differential.Use the ideal gas equation of state to verify that X is actually the internal energy and that it satisfies the above equation. Would...

Hello PF! I have some questions regarding the accumulation term for the energy balance on a variable volume system. Suppose we have a tank storing a liquid substance. The tank has a moving boundary at the top, which can expand unlimitedly. The system has a mass input \dot{m}_1 and mass output...

Homework Statement What is entropy of water at 5 Bar and an internal energy of 2724 kJkg-1? The Attempt at a Solution I have looked at the steam tables, i found where the pressure is 500kpa, then i do not know where to go from there. Thank You

Homework Statement A perfectly insulated and sealed spherical vessel contains an air-fuel mixture,somehow the mixture is made to burn causing a rise in temperature of the vessel and it's contents. Homework Equations Then which of the following is correct? A) Q=0 ,W=0...

1. One gram of water occupies a volume of 1 cm3 at atmospheric pressure. When this amount of water is boiled, it becomes 1671 cm3 of steam. Calculate the change in internal energy for this vaporization process. The heat of vaporization for water is 2.26 x 106 J/kg. 2. w = -PΔV, E = q + w...

Limestone stalactites and stalagmites are formed in caves by the following reaction: Ca2+(aq) + 2HCO3-(aq) --> CaCO3(s) + CO2(g) + H2O(l) . If one mol of CaCO3 forms at 298 K under 1 atm pressure, the reaction performs 2.48 kJ of P - V work, pushing back the atmosphere as the gaseous CO2 forms...

Homework Statement Hi, I am came across the following question and can't quite make complete sense of it: "Explain, in terms of internal energy, why a liquid cools when it evaporates". Homework EquationsThe Attempt at a Solution Could someone tell me whether this questions is implying random...

Homework Statement Internal Energy Change Homework Equations N/A The Attempt at a Solution If internal energy change equals enthalpy change, then I am looking for the reaction which has the enthalpy change closest to zero. I know it cannot be A, as the formation of water is highly exothermic...

Homework Statement Derive an expression for the change in internal energy of 1 mol of an ideal gas for expansion from volume V_i to V_f under constant pressure of 1atm where \gamma = \frac{C_p}{C_v}=\frac{5}{3} Homework Equations \Delta U=\frac{3}{2}nR\Delta T PV=nRT The Attempt at a...

So the internal energy of a system changes if work or heat is transferred between itself and its environment. Say you compress a gas and therefore do work on it, increasing its internal energy. According to Newton's 3rd law, shouldn't the gas also do work on its surroundings. How come this isn't...

Hello, From what I know, internal energy of a body = sum of kinetic energies of the particles of the body + potential energy between the particles (intermolecular forces), right? And there's this textbook question which made me question that for a while: Two objects are at the same temperature...

Homework Statement In which of the following cases does the internal energy of the described system increase: (I) A clay ball is dropped and sticks to the ground (II) Hydrogen and oxygen react exothermically to form water (III) A car is driven at constant speed (consider the effect of air...

Homework Statement For a single molecule, derive the internal energy U = 3/2kBT In terms of the partition function Z, F = -kBTlnZ Where Z = V(aT)3/2 Homework Equations Thermodynamic identity: δF = -SδT - pδV p = kBT/V S = kB[ln(Z) + 3/2]The Attempt at a Solution U = F + TS δU = δF +...

Hello, So I have been struggling to understand internal energy for quite a long time and I hope you will be able to help me get straight with it. The most common definition I find on the internet is "The sum of the kinetic and potential energy of the molecules/atoms in a system" (often gases)...

Homework Statement An assembled system consists of cart A of inertia mA, cart B of inertia mB, and a spring of negligible inertia, clamped together so that the fully compressed spring is aligned between the front end of cart B and the back end of cart A. The internal energy of the system...

I understand the main concepts around this topic but I am struggling to find any information about the potential energy involved in the latent heat of fusion. My book defines internal energy as kinetic and potential unlike an ideal gas that is assumed to have just kinetic energy. When a...

Homework Statement A glass cup with a mass of 0.1 kg and an initial temperature of 23◦C is filled with 0.3 kgof water at 80◦C A)What is the final temperature of the water and cup? B)How much heat must be added to raise the temperature to 90◦C? C) What is the change in the internal energy of...

Homework Statement A 1200-kg car is backing out of a parking space at5.5m/s . The unobservant driver of a 1900-kgpickup truck is coasting through the parking lot at a speed of 4.0m/s and runs straight into the rear bumper of the car. What is the change in internal energy of the two-vehicle...