lecture 5 Flashcards
(19 cards)
is combustion of hydrogen exo or endo
exo
what does exo mean in terms of enthalpy
decrease in enthalpy
-🔺H
is the haber bosch process exo or endo
exo
is photosynthesis endo or exo
endo - uses light energy
what does endo mean in terms of enthalpy
enthalpy increases
+🔺H
what is the second law or thermodynamics
S, entropy of an isolated system increases in the course of a spontaneous change
🔺s > 0
how does more heat mean higher entropy
more heat = more disorganised motion
= more disorder
= increase in entropy
what is entropy
measure of disorder
what are the 2 change in entropy equations
dS = dq (in a reversible process) ///// T
🔺s = integral { dq(rev) / T
limits = final state - initial state (temp)
what is 🔺S
change in entropy
what is 🔺s at a constant temperature
🔺s = 🔺q/T
what is another way of phasing the 2nd law of thermodynamics
entropy of an isolated system can never decrease
entropy of surroundings or system will increase
🔺s of universe equation
🔺s universe = 🔺s system + 🔺s surroundings
equal to or bigger than 0
what happens to entropy as u go from hot to cold
overall entropy increases
entropy decreases
HOT : ds = - dq/ T
COLD : ds = dq / T
cold to hot will always have a higher entropy as it’s not negative
what is cool about the amounts of heat gained by 2 objects
gain the same amount of heat but opposite
- 20
+ 20
how to do u go from the molar heat capacity to the total heat capacity in a reaction
multiply the molar heat capacity by the number of moles in the reaction
how do we measure reversible expansion at a constant temp
🔺q(rev) = -🔺w(rev) = nRT ln(Vf/Vi)
🔺s = 🔺q/T
we can find 🔺s even if the expansion is not done reversibly bc S is a state function
what does the 🔺s of surroundings depend on
depends on conditions
the answer for 🔺s for surroundings will be the opposite answer to the 🔺s of the system.
how do we find nr when using entropy of expanding idea gas.
use the ideal gas equation::: pv/T = nr
then use this in the gas expansion equation 💗💗
