How do delta H and q differ in thermodynamics?

In summary, delta H and q are two separate quantities that are related to each other through the equations delta H = delta U + P(delta V) and q = delta U - W. The main difference between the two is that delta H takes into account changes in pressure, while q does not. When the pressure is kept constant, the heat absorbed will be equal to the enthalpy change.
  • #1
sachin123
121
0
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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  • #2
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?
 
  • #3
Yes it does.
So only when the pressure is kept constant,the heat absorbed will become equal to the enthalpy change right?
Thanks Mapes
 

FAQ: How do delta H and q differ in thermodynamics?

What is the difference between delta H and q?

Delta H refers to the change in enthalpy of a system, while q refers to the heat exchanged between a system and its surroundings. In other words, delta H is a measure of the overall energy change in a system, while q specifically measures the transfer of thermal energy.

Can delta H and q be positive or negative?

Yes, both delta H and q can have positive or negative values. A positive delta H indicates an endothermic process, where the system absorbs heat from the surroundings. A negative delta H indicates an exothermic process, where the system releases heat to the surroundings. Similarly, a positive q indicates heat being transferred into the system, while a negative q indicates heat being transferred out of the system.

How are delta H and q related?

Delta H and q are both related to the change in internal energy of a system. They are connected by the equation q = delta H + delta nRT, where delta n is the change in the number of moles of gas and R is the gas constant. This equation is known as the heat capacity equation.

Can delta H and q have different units?

Yes, delta H is typically measured in joules (J) or kilojoules (kJ), while q can be measured in a variety of units depending on the specific situation. For example, q can be measured in joules, calories, or British thermal units (BTUs) depending on the system being studied.

How does a change in temperature affect delta H and q?

A change in temperature will affect both delta H and q. An increase in temperature will lead to an increase in both delta H and q, while a decrease in temperature will result in a decrease in both delta H and q. This is because temperature is directly related to the internal energy of a system, which is a component of both delta H and q.

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