# What is Thermodynamics heat: Definition and 24 Discussions

Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governed by the four laws of thermodynamics which convey a quantitative description using measurable macroscopic physical quantities, but may be explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, biochemistry, chemical engineering and mechanical engineering, but also in other complex fields such as meteorology.
Historically, thermodynamics developed out of a desire to increase the efficiency of early steam engines, particularly through the work of French physicist Nicolas Léonard Sadi Carnot (1824) who believed that engine efficiency was the key that could help France win the Napoleonic Wars. Scots-Irish physicist Lord Kelvin was the first to formulate a concise definition of thermodynamics in 1854 which stated, "Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency."
The initial application of thermodynamics to mechanical heat engines was quickly extended to the study of chemical compounds and chemical reactions. Chemical thermodynamics studies the nature of the role of entropy in the process of chemical reactions and has provided the bulk of expansion and knowledge of the field. Other formulations of thermodynamics emerged. Statistical thermodynamics, or statistical mechanics, concerns itself with statistical predictions of the collective motion of particles from their microscopic behavior. In 1909, Constantin Carathéodory presented a purely mathematical approach in an axiomatic formulation, a description often referred to as geometrical thermodynamics.

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1. ### I How is the derivative of an inexact differential defined?

This is from Callen's thermodynamics. What does the differentiation with respect to T means for an inexact differential like dQ. Also why is T treated as a constant if we start by replacing dQ by TdS? Any references to the relevant mathematics will be much appreciated.
2. ### Calculate the volume change with gas temperature for this piston in a cylinder

Solution attempt : Option : I am sure that my work is wrong. But, I must add solution attempt in PF that's why I just added that. How can I solve the problem?
3. ### Pump with intake and compression using different pressure ratios

Lets say we got a larger cylinder-piston combo and a smaller one. First we move the larger cylinder, filling in with vacuum. Then we pump in air, using the smaller cylinder, isothermally, with variable expansion ratio. Here, we clearly have exp ratio > P_atm/P_final We then compress the larger...
4. ### Hole in an aluminium plate and that plate is heated

the radius of the hole should decrease from my perspective but the book says that the radius of the hole will increase. I am not able to understand why??
5. ### Questions about the Point Function (Thermodynamics)

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...
6. ### There is a thermodynamics problem I cannot solve

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...
7. ### Confusion about relation of entropy with temperature.

Why can sometimes entropy remain constant with increase of temperature and vice versa?Entropy implies transfer of heat and heat must increase with temperature.I am unable to intuitively understand.
8. ### First law of thermodynamics: why some equations can't be used

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...
9. ### 2nd law of thermodynamics heat pump problem

Homework Statement Here is the problem: An inventor claims to have developed a heat pump that provides a 180 kW heating effect for a 293 K household while only consuming 70 kW of power and using a heat source at 273 K. Can this claim be possible? Homework Equations COP of heat pump = Qh/W COP...
10. ### Thermodynamic properties - Isochronic process - First law

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...
11. ### When is ΔH = ΔU in Thermodynamics?

In thermodynamics when can we say that ΔH = ΔU?
12. ### Why Temperature Depends on Internal Energy, Not Pressure/Volume

Why temparature is only dependent on internal energy of something, say an ideal gas.
13. ### Thermodynamics adiabatic diffuser question

An adiabatic diffuser is employed to decrease the velocity of an airstream from 220 to 30 m/s. The air enters the diffuser at a rate of 8 kg/s with a temperature of 300c and a pressure of 100kpa. Determine the exit area of the diffuser if the exit pressure is 125kpa. Answer is 0.37 m^2 Guys I...
14. ### Thermodynamics heat loss fridge

Hello To calculate the heat loss of a fridge, do I need to take the surface area of the in- or outside of the fridge? Heat loss formula = k * delta T * A k = heat transmission coefficient A = surface area
15. ### Can Calculating Ocean Bottom Temperature Enable Efficient Heat Engine Operation?

Homework Statement A haet engine works based on the difference of the temperature at the top and bottom of the ocean. The machine is solar powered and the average solar irradiance is 240W/m^2 and the temperature at the surface of the water is 25ºC. Calculate the temperature at the bottom of...
16. ### Thermodynamics Heat Radiation Problem

Hi everyone, I am unsure about how to solve this problem. I believe i have the right equation but I'm confused about how I can find Q/T with the information I am given. Is there another equation I can use? Homework Statement Assume the steel in the body of an automobile has an emissivity of...
17. ### Efficient Heat Pump Calculation for 15,000kWh Heat Output

A heat pump that used R-22 operates as shown below. Assume SEER=1.15*EER. Find the amount of work that has to be put into the system to generate 15,000kwh of heat energy.
18. ### Thermodynamics heat engine Question

Homework Statement A 1500kW heat engine operates at 25% efficiency. The heat energy expelled at the low temperature is absorbed by a stream of water that enters the cooling coils at 20 degrees C. If 60L flows across the coils per second, determine the increase in temperature of the water...
19. ### Thermodynamics heat sink questions

1.Task is to maintain the temperature a device, lower than 40 C. The unit is operating for 5 minutes and then turned off for a time period that the device temperature reaches ambient temp 25 C. Suppose you have 10 heat sinks of different weights...0.1,0.2,0.3,...1.0 kg. Determine the temperature...
20. ### How to Calculate Net Heat Transfer in an Isochoric Process

Hi, I'm really struggling with a thermodynamics coursework question, I'm not looking for the answer straight up, just wondering how to go about solving the problem as it's been racking my brain for a stupid amount of time. Here's the problem I've been given: Shaft work (500kJ/kg) is...
21. ### Thermodynamics heat transfer problem

Homework Statement An 85kg yachtsman falls out of his boat into the cold ocean waters. He begins to loose body heat through a 0.02m thick layer of surface fat. The surface heat transfer coefficient between his skin and the sea water is 30. The total surface area of the yachtsman is 2.2 and...
22. ### Thermodynamics Heat Calculation Problem

Calculate the heat that must be supplied to a 500g copper kettle containig 750 g of water to raise its temperature from 23 degrees to the boiling point of water, 100 degrees. q=MCT qwater= 750 x 4.184 x 77= 241626 J qcopper= 550 x .38 x 77= 16093 J 241626 + 16093 = 257719 J...
23. ### Thermodynamics heat absorption problem

Homework Statement How much heat is absorbed in changing 2-kg of ice at -5°C to steam at 110.0°C? The Specific heats of ice, liquid water, and steam are, respectively, 2060 J/Kg x K, 4180 J/Kg x K, and 2020 J/Kg x K. The heat fusion of ice is 3.34 x 10^5 J/Kg. The heat of vaporization of...
24. ### Thermodynamics Heat Engine Problem

Thank you in advance... 1. Homework Statement Suppose a power plant delivers energy at 918MW using steam turbines. The steam goes into the turbines superheated at 626K and deposits its unused heat in river water at 286K. Assume that the turbine operates as an ideal Carnot engine. If the...