Thermodynamics Heat Work Definition, Similarities, Differences

Thermodynamics Heat Work Definition

Heat Definition

  • The temperature difference between system and surroundings.
  • This exchange of heat takes place through thermally conducting walls (boundary).
  • If the temperature of a system is higher than the surrounding, heat is lost from the surrounding and heat is gained when the system has a lower temperature than the surrounding.
  • So, the amount of heat that is gained or lost by the system is symbolically represented by q.
  • ‘q > 0’ is positive (+ve) when the system gains or absorbs heat.
  • ‘q < 0’ is negative (-ve) when the system loses heat.

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Work Definition

  • The energy between system and surroundings can take place in the form of work which may be mechanical, pressure-volume or electrical.
  • For example, Take a thermos flask (thermally insulated) with some water in it and note down its temp., after doing some work (mechanical) by inserting a paddle and rotating it we will notice an increase in temp. This indicates the increase in internal energy, i.e., gaining energy by the system by doing work on it.
  • The work done by the system or on the system is denoted by ‘w’.
  • Work is positive (w>0) when done by the system.
  • Work is negative (w<0) when done on the system.
  • The pressure-volume work is also called expansion work.

Heat and Work Similarities

  •  Work and Heat, both are a transient phenomenon, i.e. these cross the boundaries of the system whenever system undergoes a change of state
  • Heat and Work are observed at the boundaries of the system.
  • Heat and Work are path functions
  • Both are inexact differentials.

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Heat and Work Differences

  • When heat is added, molecules start moving in different directions and thus, the system attains randomness whereas when work is done molecules attain an order.
  • Hence, work can be regarded as an organized form of energy and heat as a random form of energy.
  • Work is high-grade energy whereas Heat, is low-grade energy.

Note- In a few texts convention for work is opposite as mentioned above.

S, we hope you liked this brief thermodynamics Heat Work Definition. This will surely help you in excelling in the GATE Exam.

Read Also: GATE Syllabus for Mechanical Engineering

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