How do delta H and q differ in thermodynamics?

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SUMMARY

The discussion clarifies the distinction between delta H (enthalpy change) and q (heat transfer) in thermodynamics. It establishes that delta H is defined as delta U (internal energy change) plus the product of pressure and change in volume (P(delta V)). The relationship is further detailed with the equation delta U = q + W, leading to q = delta U - W. It is confirmed that delta H equals q only under constant pressure conditions, emphasizing the importance of pressure in thermodynamic calculations.

PREREQUISITES
  • Understanding of thermodynamic concepts such as internal energy and work
  • Familiarity with the first law of thermodynamics
  • Knowledge of enthalpy and its mathematical representation
  • Basic grasp of pressure-volume work in thermodynamic systems
NEXT STEPS
  • Study the first law of thermodynamics in detail
  • Learn about the conditions under which enthalpy change equals heat transfer
  • Explore the implications of constant pressure processes in thermodynamics
  • Investigate the role of work in thermodynamic systems and its relation to internal energy
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This discussion is beneficial for students of thermodynamics, chemical engineers, and anyone involved in physical chemistry who seeks to understand the relationship between heat transfer and enthalpy changes in various processes.

sachin123
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what is the difference between delta H and q?
delta H = delta U + P(delta V)
so,
delta H = delta U -W

delta U=q + W
so,
q=delta U - W

So now is there a difference between the two at all?
Why then 2 separate quantities?
Thank You
 
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sachin123 said:
delta H = delta U + P(delta V)

You fixed P to get this expression, so you're no longer looking at the most general case. Does this help answer your question?
 
Yes it does.
So only when the pressure is kept constant,the heat absorbed will become equal to the enthalpy change right?
Thanks Mapes
 

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