lecture 5

Question 1

is combustion of hydrogen exo or endo

Answer 1

exo

Question 2

what does exo mean in terms of enthalpy

Answer 2

decrease in enthalpy
-🔺H

Question 3

is the haber bosch process exo or endo

Answer 3

exo

Question 4

is photosynthesis endo or exo

Answer 4

endo - uses light energy

Question 5

what does endo mean in terms of enthalpy

Answer 5

enthalpy increases
+🔺H

Question 6

what is the second law or thermodynamics

Answer 6

S, entropy of an isolated system increases in the course of a spontaneous change

🔺s > 0

Question 7

how does more heat mean higher entropy

Answer 7

more heat = more disorganised motion

= more disorder
= increase in entropy

Question 8

what is entropy

Answer 8

measure of disorder

Question 9

what are the 2 change in entropy equations

Answer 9

dS = dq (in a reversible process) ///// T

🔺s = integral { dq(rev) / T

limits = final state - initial state (temp)

Question 10

what is 🔺S

Answer 10

change in entropy

Question 11

what is 🔺s at a constant temperature

Answer 11

🔺s = 🔺q/T

Question 12

what is another way of phasing the 2nd law of thermodynamics

Answer 12

entropy of an isolated system can never decrease

entropy of surroundings or system will increase

Question 13

🔺s of universe equation

Answer 13

🔺s universe = 🔺s system + 🔺s surroundings

equal to or bigger than 0

Question 14

what happens to entropy as u go from hot to cold

Answer 14

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

Question 15

what is cool about the amounts of heat gained by 2 objects

Answer 15

gain the same amount of heat but opposite

• 20
  + 20

Question 16

how to do u go from the molar heat capacity to the total heat capacity in a reaction

Answer 16

multiply the molar heat capacity by the number of moles in the reaction

Question 17

how do we measure reversible expansion at a constant temp

Answer 17

🔺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

Question 18

what does the 🔺s of surroundings depend on

Answer 18

depends on conditions

the answer for 🔺s for surroundings will be the opposite answer to the 🔺s of the system.

Question 19

how do we find nr when using entropy of expanding idea gas.

Answer 19

use the ideal gas equation::: pv/T = nr

then use this in the gas expansion equation 💗💗