## qp and qv

Diana_Diep2I
Posts: 130
Joined: Sat Aug 17, 2019 12:17 am

### qp and qv

Why is qp=∆H and not qv?

Abby Soriano 1J
Posts: 103
Joined: Sat Aug 24, 2019 12:16 am

### Re: qp and qv

By definition, enthalpy is the amount of heat absorbed/released at a constant pressure. So that means that delta H only equals qp rather than qv.

Sjeffrey_1C
Posts: 108
Joined: Wed Feb 20, 2019 12:17 am

### Re: qp and qv

Enthalpy in this case is referring to heat at a specific pressure, not a specific volume. Thus, the p subscript instead of v.

Hailey Kim 4G
Posts: 110
Joined: Sat Jul 20, 2019 12:16 am

### Re: qp and qv

Enthalpy, which is represented by delta(h), is heat at a constant pressure. Heat is represented by "q", and because the pressure is constant, it will have the subscript "p" for pressure, rather than "v" for volume.

Posts: 116
Joined: Thu Jul 25, 2019 12:15 am

### Re: qp and qv

When volume is not constant, the gas is either expanding or compressing, so there is some work done. Therefore, that energy from work contributes to the delta H and must be factored in.

Sydney Myers 4I
Posts: 100
Joined: Fri Aug 09, 2019 12:17 am

### Re: qp and qv

It's simply that the definition of enthalpy is heat at a constant pressure. That's how it's defined as a function.

Junwei Sun 4I
Posts: 125
Joined: Wed Oct 02, 2019 12:16 am

### Re: qp and qv

Because by definition H is the heat transferred at constant pressure.

Maya Pakulski 1D
Posts: 105
Joined: Thu Jul 11, 2019 12:17 am

### Re: qp and qv

This is because by definition delta H only equals q at constant pressure.

Orrin Zhong 4G
Posts: 51
Joined: Sat Jul 20, 2019 12:16 am

### Re: qp and qv

If the heat transfer is occurring while pressure is changing, q is not equal to change in enthalpy, since the change in enthalpy is defined at a constant pressure. Therefore, change in enthalpy only equals q when pressure is held constant: qp = change in enthalpy.