What is Thermodynamics first law: Definition and 32 Discussions
The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes, distinguishing two kinds of transfer of energy, as heat and as thermodynamic work, and relating them to a function of a body's state, called internal energy.
The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.
For a thermodynamic process without transfer of matter, the first law is often formulated
Δ
U
=
Q
−
W
{\displaystyle \Delta U=Q-W}
,where
Δ
U
{\displaystyle \Delta U}
denotes the change in the internal energy of a closed system,
Q
{\displaystyle Q}
denotes the quantity of energy supplied to the system as heat, and
W
{\displaystyle W}
denotes the amount of thermodynamic work done by the system on its surroundings. An equivalent statement is that perpetual motion machines of the first kind are impossible.
For processes that include transfer of matter, a further statement is needed: 'With due account of the respective reference states of the systems, when two systems, which may be of different chemical compositions, initially separated only by an impermeable wall, and otherwise isolated, are combined into a new system by the thermodynamic operation of removal of the wall, then
U
0
=
U
1
+
U
2
{\displaystyle U_{0}=U_{1}+U_{2}}
,where
U
0
{\displaystyle U_{0}}
denotes the internal energy of the combined system, and
U
1
{\displaystyle U_{1}}
and
U
2
{\displaystyle U_{2}}
denote the internal energies of the respective separated systems.'
Hi, as follow up to this thread I believe for any substance/thermodynamic system there exists actually a set of 3 state equations between the 5 variables ##(U,T,S,p,V)##.
For example in the case of ideal gas which are the 3 equations ? Thanks.
TL;DR Summary: Struggling to structure the problem and derive an analytical solution for gas expanding into other gas in a rigid tank. Preferred formulation is fixed control volumes. This is not a homework problem.
The problem:
Two control volumes (A and B) are in a rigid tank filled with air...
Hello everyone, since several weeks, no response from the other forums, I tried to compute a simple model for a greenhouse in a garden. First idea was to compute mass transfer, Navier-Stokes and heat equation all together but in my knowledge no analytical solution exists.I need to build a simple...
For the first part, I have expressed it in the following differential form- dU= delta (Q) + BdM
Now for the second part I am having major confusion. I know that B corresponds to P and M corresponds to V as generalised force and generalised displacement respectively for a Paramagnetic substance...
So I calculated the final and initial pressures using the given eqns, ended up with the final pressure of 96629 and initial pressure of 62639.
Then I used the PV=nRT eqn to calculate the final and initial temperatures. T=P*V/(n*1.5*R).
I got an initial temperature of 81.79 and a final...
In this problem, the method used to solve the question is to equate pdV with change in internal energy. This implies an adiabatic process as Q = 0? (not sure about this claim) However, why is it not correct to simply apply the PV^ϒ = constant formula?
Thank you.
I am looking for help on the following:
a) Given the system shown in the figure below, derive the steady flow energy equation from first principle.
b) Again using first principles, show how the energy equation would change for the case when the system is unsteady.
I am trying to learn this...
Why is energy balance for a control volume
dE/dt = dQ/dt-dW/dt-dm/dt(ΔH+ΔKE+ΔPE)
0 = dQ/dt-dW/dt-dm/dt(ΔH+ΔKE+ΔPE)
whereas for other systems it is
ΔE =Q-W-(ΔU+ΔKE+ΔPE)
0 = Q-W-(ΔU+ΔKE+ΔPE)
with enthalpy, h = u +pv, replaced by only the internal energy? How is the pv term accounted for...
We know from first law of thermodynamics for a closed system that ##dE##=##\delta Q## -##\delta W## , my question is that for a closed adiabatic system net heat transfer =0 this mean net change in energy = work done , does that mean for an adiabatic system work done is a point function as...
Precursor : Sign conventions regarding Work by the system/on the system may even vary among Physics textbooks and among Chemistry textbooks and as a rule of thumb it is better to clearly mark out the convention used by the text being referred to specifically and remain consistent with it...
Homework Statement
A monoatomic ideal gas undergoes a linear process whose equation is given by P/po+V/vo=1. find the volume when the process turns from an exothermic to an endothermic one. P-Pressure V-volume
Po= pressure when volume is nearly 0 and Vo is the volume when pressure is...
When an ideal gas,in a piston kind of system and whose equilibrium state is mentioned, is allowed to expand (piston is allowed to move and not gas leaking )against a constant external pressure very quickly, then, is the work done by gas zero or not zero ?
The argument for work being zero is...
1.
Consider a balloon which has thick rigid walls and
from which all the air has been pumped out. Now, the valve of
the balloon is slightly opened, and the balloon is slowly filled
with the air from outside. Find the temperature of the air
inside the balloon once the air flow has stopped (since...
Homework Statement
12kg of a fluid per minute goes through a reversible steady flow process. The properties of fluid at the inlet are p1 = 1.4bar, ρ1 = 25kg/m3, C1= 120m/s and u1= 920kJ/kg and at the exit are p2= 5.6bar, ρ
2= 5 kg/m3, C2= 180m/s and u2
Homework Equations
u1 + P1V1 + (C1)2/2 +...
So, I have noticed that when people are crowded in small rooms, it feels hot. In fact, everyone in the crowd feels hot and starts sweating. I am wondering about the origin of all this heat.
I do know that by first law of thermodynamics, if two people touch each other and if one of them feels...
< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown >
Hey,
For our project we have to think of an experiment that can kind of simulate a rocket. We decided to use a fire extinguisher on a kart, since its mass constantly changes (same with a rocket)...
Homework Statement
A spring (k = 500 N/m) supports a 400 g mass which is immersed in 900 g of water. The specific heat of the mass is 450 J/kg and of water is 4184 J/kg. The spring is now stretched 15 cm and, after thermal equilibrium is reached, the mass is released so it vibrates up and...
Homework Statement
By applying the first law to a quasi static process, show that the entropy can be expressed as
S = (16σ/3c) VT3
Homework Equations
U = 4(σ/c) VT4
PV = 1/3 U[/B]The Attempt at a Solution
I know I should be using
dS = dQ/T but it's unclear to me how to use this unless I...
Homework Statement
A cylinder fitted with a frictionless piston contains 5.0×10-4m3 of an ideal gas at a pressure of 1.0×105 Pa and temperature of 300K.
The gas is then
(i) heated at constant pressure to 450K, and then
(ii) cooled at constant volume to the original temperature of 300K. The...
Homework Statement
55. Solid A, with mass M, is at its melting point TA. It is placed in thermal contact with solid B, with heat capacity CB and initially at temperature TB (TB > TA). The combination is thermally isolated. A has latent heat of fusion L and when it has melted has heat capacity...
Homework Statement
We have
0.0008 Kmol of an ideal gas are expanded from V1 to V2 v2=3V1
process is reversible and T/V=Constant
if the work obtained by this expansion is 9.4 KJ find the initial temperature
R=8.314 KJ Kmol-1
Homework Equations
PV=nRT
possibly T/V = T/V
The Attempt at a...
Homework Statement
An amount of water substance having a mass of 1 kg is contained in a vessel at a pressure of 1 MPa. It is heated for some time after which the pressure is 3 MPa. The volume of the vessel is 0.1 m3. Assuming no work is done by or to the substance, calculate the final...
Homework Statement
Can someone help me confirm if I answered correctly please?
a) A sample of gas is enclosed in a cylinder by a piston. The cylinder is given 225J of energy which expands and pushes the piston 16cm outwards against an atmospheric pressure of 1.01x105Pa.
i) give the equation...
Homework Statement
In an adiabatic steam nozzle,steam is expanded from 10 bar and 473k to an exit pressure of 5 bar.nozzle has an isentropic efficiency of 90%.neglect kinetic energy at the inlet.assuming equilibrium condition at exit,find the velocity of nozzle at exit? given data : i)at nozzle...
Homework Statement
Consider a rock having a mass of 5 kg and a bucket containing 50 kg of liquid water. Initially, the stone is 20 m above the water, and the stone and the water are at the same temperature, T1 (state 1). The stone then falls into the water.
For the system stone + water...
Homework Statement
Consider a system consisting of 2.0 mol CO2 (assumed to be a perfect gas) at 298K confined to a cylinder of cross-section 10cm^2 at 10 atm. The gas is allowed to expand adiabatically and reversibly against a constant pressure of 1 atm. Calculate W, Q, ΔU, ΔH, and ΔT when the...
one mole of monatomic gas (in a perfectly insulated cylinder)
has temp = 27 degees c = 300K
volume = 0.025m^3
(gas held in frictionless piston)
heat suppied causes gas to expand at constant pressure gas expands to volume = 0.06m^3
i) calc final temp..
i used pV/T =pV/T (p cancels...