# Thermodynamics closed system - first law

• meanmachine
In summary, The problem involves determining the total work done during a process where 1kg of water initially at 90 degrees celsius with a quality of 10% is heated in a spring loaded piston cylinder device until the pressure reaches 800kPa and the temperature is 250 degrees celsius. The first law for closed systems is applied, with states 1 and 2 being a saturated mixture and superheated vapor, respectively. The change in internal energy is calculated and the work is determined to be incorrect, requesting assistance.
meanmachine

## Homework Statement

1kg of water that is initially at 90 degrees celsius with a quality of 10% occupies a spring loaded piston cylinder device. The device is now heated until the pressure rises to 800kPa and the temperature is 250 degrees c
Determine the total work done during this process, in KJ

## Homework Equations

The first law for closed systems
Q - W = ΔU
(h2-h1 - u2 - u1) = ΔU

## The Attempt at a Solution

State 1

Saturated mixture (90 degrees)
x = 0.1
H1 = 605.29 KJ/kg
U1 = 588.67 KJ/kg

State 2 - super heated vapour

h2 = 2950.4 KJ/kg
u2 = 2715.9 KJ/kg

therefore,

ΔU = (2950.4 - 605.29) - (2715.9 - 588.67) = 217.88 KJ

which is incorrect, can you assist me with this question?

You would actually just need to apply

W = m(h2-h1)

remember that enthalpy h includes internal energy u.

## What is a closed system in thermodynamics?

A closed system is a thermodynamic system that does not exchange matter with its surroundings, but can exchange energy in the form of heat or work.

## What is the first law of thermodynamics?

The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, but can only change forms or be transferred from one system to another.

## How is the first law of thermodynamics applied to a closed system?

In a closed system, the first law of thermodynamics can be expressed as: the change in internal energy of the system is equal to the heat added to the system minus the work done by the system.

## What is the significance of the first law of thermodynamics?

The first law of thermodynamics is significant because it is a fundamental principle of energy conservation and forms the basis of all thermodynamic processes.

## How is the first law of thermodynamics related to the concept of entropy?

The first law of thermodynamics and the concept of entropy are closely related, as they both deal with the transfer and transformation of energy in a closed system. Entropy can be thought of as a measure of the disorder or randomness of a system, and the first law of thermodynamics states that the total amount of energy in a closed system remains constant, but it can change forms and become more disordered.

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