[madscientist]

in a product favoured process,

the expansion of an ideal gas,

is this an endothermic process?

im 90% sure that it is but just need it confirmed.

cheers,

madscientist

[Yggdrasil]

Under what conditions are you expanding the ideal gas?  The answer will differ depending on the conditions under which you perform the expansion (e.g. isobaric, isothermic, adiabatic, etc).

[madscientist]

good point,

the question doesnt state under which conditions the expansion takes place??

Question states:

Of the following product favoured processes, which are endothermic?

1.) the combustion of methane to produce carbon dioxide and water

2.)the expansion of an ideal gas

3.)the melting of ice at temperatures abvove 0^oC

choices are:

a.) 1 only

b.)2 only

c.) 3 only

d.)1 and 2

e.)2 and 3

now i know that 3 is endo thermic so that wipes out choice 1, so its not a b or d, therefore am only left with c and e

[Yggdrasil]

Ok, if that's the question, I guess you can assume it means isobaric expansion.  Technically, an endothermic reaction is defined as a reaction with a positive change in enthalpy and enthalpy's practical definition is heat gained/lost at constant pressure.  From the ideal gas law (PV=nRT), you see that at constant pressure and constant number of molecules, temperature must increase for volume to increase.  Therefore, you can say that the expansion of an ideal gas is an endothermic process.