# What is Thermodynaics: Definition and 11 Discussions

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1. ### B Can we use molecular speed of gas formula also for the air?

Molecular speed of gas is generally $$v=\sqrt{\frac{3RT}{M}},$$where R is gas constant and M is molecular mass. Can we use this formula for the air as well, when the air is a mixture of different gasses?
2. ### Engineering Carnot Cycle and Coefficient of Performance

I think I calculated part a correctly by extracting the cp (specific heat) of water from the table which is 4.188 Then calculated Q_dot by simply using the equation Q=m*c*deltaT=10.47kW But I am stuck at part b, I know that the heat extracted from the water is the same as Q_L (rate of heat...
3. ### How can I calculate the drop in pressure across an orifice?

I know the inlet pressure, temperature and density along with the massflow rate across the orifice and the orifice cross section. Is there a way for me to calculate the drop in pressure across the orifice?
4. ### Relationship between ln k and 1/t using different formula

Hi, I'm currently taking Chemistry 101 and came across this equation that seems to contradict what I've learned before. I don't know the name of it, but here is the equation and its implication. Now another equation we have learned is the Arrhenius equation, which is as follows: If I...
5. ### Entropy Change in Free Expansion: Why △S=ncᵥln(T_f/T_i)+nRln(V_f/V_i)?

In a free expansion, I know that we cannot use the equation dS=dQ/T...(1). Instead we use dS>dQ/T...(2). The question is that why we can use △S=ncᵥln(T_f/T_i)+nRln(V_f/V_i) , which is derived from the equation(1), to calculate the entropy change? Shouldn’t it be a inequality too?
6. A

### Why is the work done considered negative in this thermodynamics problem?

<Moderator's note: Approved although without template. Member has been warned.> An ideal gas is taken along the path AB (see fig.). If 70 calories of heat is extracted from the gas during the process, calculate the change in internal energy during the process. My attempt : Work done in the...
7. ### How to find the thermal compressibility of a gas

Homework Statement : [/B] A gas obeying the equation of state PV=RT undergoes a hypothetical reversible process PV^\frac{5}{3} e^\frac{-PV}{E_0} = c_1 Can we prove that the thermal compressibility of the gas undergoing this process tends to a constant value at very high temperature? Here, E_0...
8. ### I Liquid boiling and Evaporation

In the normal conditions (sea level) water evaporates at 100 C. In thermodynamics, we say: the amount of energy Q, can raise temperature of the liquid by the formula Q1=cm(t2-t1); when the liquid reaches the boiling point (100 C), we write Q2=Lm. Q2 is entirely spent on changing liquid state...
9. ### Pressure reported from a water line, gauge or absolute?

Homework Statement Homework EquationsThe Attempt at a Solution I thought the pressure in a water line is in gauge pressure, but the solution suggests that 1630 kPa is in absolute pressure, do we always assume absolute pressure unless otherwise specified?
10. ### Thermodynaics Analysis of Processes

Homework Statement A cylinder, A, having Va=30L, is connected to a second cylinder B, of circular cross section. Cylinder B is fitted with a piston of radius = 5cm, which slides without friction/leaking. Initially A contains an ideal monatomic gas, in addition, Pa = 10MPa, Ta = 300K, Vb = 0...
11. ### Thermodynaics, solving for minimum power to heat water

An electric hot water heater takes in cold water at 15.8°C and delivers hot water. The hot water has a constant temperature of 45.6°C, when the "hot" faucet is left open all the time and the volume flow rate is 5.0 multiplied by 10-6 m3/s. What is the minimum power rating of the hot water...