Thermodynamics - Work/Heat question

In summary, the conversation discusses a question in a coursework about a system of gas contained in a cylinder undergoing a process from state b to state a. The person has done the question simply and is wondering if they have missed something. They mention that 50 J of heat flow out of the system and 25 J of work is done on the system. They ask for help in determining how much work is done and if it is done on or by the system when the system follows a different path and 40 J of heat is expelled. The person also mentions the equation DQ=-DW and wonders if it applies in this case. The other person suggests considering the change in internal energy and asks about equations relating internal energy, heat, and work
  • #1
Milsomonk
96
17
Hi guys,
So I have a question in a piece of coursework which I seem to have done too simply, its worth 7 marks and I am thinking I've missed something somewhere so was hoping to run it by someone else.

1. Homework Statement

A system consists of gas contained in a cylinder fitted with a frictionless piston and
is taken from the state b to the state a along the path b  d  a shown in the
figure below. During this process 50 J of heat flow from the system and 25 J of
work is done on the system.
upload_2015-10-25_14-55-10.png

How much work is done when the system is taken along the path b  c  a if
40 J of heat are expelled by the system? Is it done on or by the system?

Homework Equations


DQ=-DW

The Attempt at a Solution


I have simply said that since 40J of heat flows from the system, 40J of work is done on the system. Due to the above equation. My only thought is that perhaps this equation doesn't hold for B to C to A since the path is not closed? If anyone can point me in the right direction I would be very grateful :)
Thanks
 
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  • #2
Think about the change in internal energy of the system. What equations do you know that relate internal energy, heat and work?
 

Related to Thermodynamics - Work/Heat question

What is the difference between work and heat in thermodynamics?

Work and heat are both forms of energy transfer in thermodynamics, but they differ in how they are transferred. Work is the transfer of energy through mechanical means, such as pushing or pulling an object. Heat is the transfer of energy due to a temperature difference between two objects.

How is work calculated in thermodynamics?

The formula for work in thermodynamics is W = Fd, where W is work, F is the force applied, and d is the distance over which the force is applied. In other words, work is equal to the product of force and distance.

What is the first law of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. This law is also known as the law of conservation of energy.

Can work be negative in thermodynamics?

Yes, work can be negative in thermodynamics. This occurs when work is done on a system, meaning that energy is transferred into the system. On the other hand, work done by a system results in a positive value, indicating that energy is being transferred out of the system.

How does thermodynamics relate to real-world applications?

Thermodynamics is a fundamental concept in many real-world applications, such as power plants, refrigeration systems, and engines. It helps us understand and optimize the transfer and conversion of energy in these systems, leading to more efficient and sustainable technologies.

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