Heat/Phase Change Terminology

[MedPR]

What is the difference between isothermal and adiabatic?

Isothermal = no change in energy, adiabatic = heat in=heat out?

Also, I just read this in EK Gen Chem and it doesn't make sense to me.

In an isothermal expansion of a gas, we can expand a gas at constant temperature by adding heat during the expansion.

If you are adding heat, how can it be isothermal?

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[chiddler]

isothermial means the temperature doesn't change. adiabatic means there is no energy exchange.

now does it make sense?

 

[MedPR]

isothermial means the temperature doesn't change. adiabatic means there is no energy exchange.

now does it make sense?

Kind of. Isothermal means that you can put in energy, but all of that energy must go to PV work if it is to be considered isothermal?

I'm not really clear on how adiabatic works. If there is no energy exchange, then how does anything change? Work is energy exchange, temperature change is energy exchange...

 

[chiddler]

Kind of. Isothermal means that you can put in energy, but all of that energy must go to PV work if it is to be considered isothermal?

I'm not really clear on how adiabatic works. If there is no energy exchange, then how does anything change? Work is energy exchange, temperature change is energy exchange...

Isothermal means temperature doesn't change as volume or pressure changes. eg, increase volume causes temperature to drop. so to make it isothermal, an amount of energy is added to keep T the same.

what do you mean it must go to "PV work"? (as opposed to what?)

Adiabatic, on the other hand, is the above situation but without adding energy to keep T the same. So increasing volume in adiabatic conditions will yield a lower temperature.

More mistake from me: I said adiabatic means no ENERGY exchange. It should be no heat exchange. Sorry. That's #3 today >.>. least i'm learning, too.

 

[MedPR]

Isothermal means temperature doesn't change as volume or pressure changes. eg, increase volume causes temperature to drop. so to make it isothermal, an amount of energy is added to keep T the same.

what do you mean it must go to "PV work"? (as opposed to what?)

Adiabatic, on the other hand, is the above situation but without adding energy to keep T the same. So increasing volume in adiabatic conditions will yield a lower temperature.

Internal energy = heat + work. If you input heat and the temperature goes up, then the heat you put in must be converted into work (PV work is just work causing a change in pressure or volume).

So adiabatic means that total energy doesn't change, but energy converts between temperature and work?

 

[chiddler]

Internal energy = heat + work. If you input heat and the temperature goes up, then the heat you put in must be converted into work (PV work is just work causing a change in pressure or volume).

So adiabatic means that total energy doesn't change, but energy converts between temperature and work?

i edited a little bit late. check out the last sentence of comment you quoted.

adiabatic is Q = 0, ΔU = ΔW

 

[MedPR]

i edited a little bit late. check out the last sentence of comment you quoted.

adiabatic is Q = 0, ΔU = ΔW

Ok now I'm more confused. You said earlier that if you expand the system without adding heat, the temperature in the system will decrease. Makes sense. How can there be no heat change if there's work done?

Ok let's see. Found this ok mcat-review.

Adiabatic process: no heat exchange, q = 0. ΔE = W
Isothermal process: no change in temperature ΔT = 0.
Isobaric process: pressure is constant, W = PΔV.
Isovolumetric (isochoric) process: volume is constant, W = 0. ΔE = q

So an adiabatic process results in an internal energy change as a result of work being done on or done by the system. The internal energy changes because there is no heat being added or lost to compensate for the work being done. Adiabatic means no heat is being added, but the heat within the system is being converted to work.

Isothermal means whatever heat is being dissipated or added as a result of work is counteracted by adding or removing heat from the system. Isothermal means the temperature within the system remains constant, NOT temperature added or removed = 0.