Entropy
Hess's Law
Standard Enthalpy of Formation & Bond Energy
Definitions and Concepts
100
An iron bar is heated from 40°C to 80°C and does not melt. In this case, the entropy is doing this:
A) What is increasing?
B) What is decreasing?
C) What is not changing?
What is increasing?
100
2Cu (s) + O2 (g) --> 2CuO (s)
This value is the ∆H°rxn.
What is -157.3 kJ/mol?
100
This number of kJ/mol is the ∆H°f of Cl2 gas.
What is 0?
200
Is entropy a state function?*
Yes
200
This is the meaning of bond energy as used in problems such as the ones we went over in class.
What is the energy required to break the bond between two atoms?
200
The change in altitude between the base and the summit in this image is an example of this concept we discussed.
What is a state function?
300
As molten rock cools from a liquid to a solid after being exposed to air, the ∆H is this (+/-) and the ∆S is this (+/-).
What are negative & negative?
300
This value is ∆H for the missing reaction using Hess's Law.
What is -44 kJ/mol?
300
When calculating ∆H°rxn, we subtract ∆H°f reactants from ∆H°f products for this reason.*
∆H°f is the standard enthalpy of formation, but the reactants are being broken apart, not forming.
300
This is the pressure at STP (Standard Temperature & Pressure).
What is 1 atm?
400
In the equation
2H2 (g) + O2 (g) --> 2H2O (g)
is ∆S positive or negative?*
Negative
400
This value is ∆H for the following reaction using Hess's Law.
What is -2717.5 kJ
400
6H2O + 6CO2 --> C6H12O6 + 6O2
This value is the approximate molar enthalpy for this reaction.
What is 2031 kJ/mol?
400
Bond energy is always positive & endothermic for this reason.*
Bonds need to be broken which requires energy input.