Help! Please! (1 Viewer)

[Shiloh]

I am desparately neediing information on Enthalpy and Dilution. If anyone as any info whatsoever I would be soooooo unbelievably grateful!

 

[xiao1985]

enthalpy is the internal energy change of the reaction...
if change in enthalpy is negative, then it means that the total internal energy of the products is less than taht of the reactants... therefore the reaction is exothermic...
if converse is true then the reaction is endothermic...

dilution... well i thought that would be straight forward? u put in 1 ml of 1M stuff in , add 99 ml of water, u get a soln of 0.01M, easy calculation might be:
M1V1 = M2V2, though i recommend u to remmeber the idea behind the eqn... ie, calculate number of moles present, then divide it by volume to find the molarity...

 

[thunderdax]

enthalpy change=Heat change/number of moles
Heat=mass*change in temp*c
(c is 4.18 for water, which is what you'll get in any question)

 

[Will Hunting]

enthalpy is the internal energy change of the reaction...
if change in enthalpy is negative, then it means that the total internal energy of the products is less than taht of the reactants... therefore the reaction is exothermic...
if converse is true then the reaction is endothermic...

Note that enthalpy, in denotative terms, describes the heat content of a system, whereas an enthalpy "change" describes what xiao's just written (or, the thermal energy absorbed or liberated by a reaction). Make sure to watch out for confusion that may arise when comparing a "temperature" change to an enthalpy change. Even though an exothermic reaction involves a heat loss, the experimenter will register this as a temperature increase. This is because when you are are taking a measurement of temperature, you are measuring heat levels in the system's surroundings, rather than the heat changes experienced by the actual reaction participants.

enthalpy change=Heat change/number of moles
Heat=mass*change in temp*c
(c is 4.18 for water, which is what you'll get in any question)

Yep, bro, but remember that in this case, enthalpy change is measured in units of KJ/mol, heat change in KJ and number of moles in... hmmm? (J can be substituted for KJ, but enthalpy change is usually expressed in the former way). Thunder's next equation comes from AH = MCgAT (where A is change). Note that the sign for an enthalpy change is the REVERSE of the sign for heat of combustion. For example, an exothermic reaction will yield a negative value for enthalpy change, since heat has been lost by the system, but a positive value for heat of combustion, since heat has been gained by the surroundings.

Ah denotes enthalpy change
Ahc subscripted denotes heat of combustion (I still don't have that sub/super script thing down )

Good luck with this, man