Polar Bonds and Molecules
No
What is the strongest intermolecular force?
ion-dipole
What is enthalpy?
energy as heat
What CAN change according to Hess' Law
the reaction pathway
What are standard conditions?
P = 1 atm
T = 25ºC or 298.15 K
Is the bond between H and Br polar?
Yes
Which intermolecular force is present between all molecules?
dispersion forces
Is baking bread an exothermic or endothermic reaction?
What CANNOT change according to Hess' Law?
The change in enthalpy.
What is the standard enthalpy of formation of solid copper?
0 kJ/mol
Is water a polar molecule?
Yes
What is the strongest IMF NH3 could form with itself?
hydrogen bonds
When you bake bread, what is the system?
the bread
Determine the correct modification to the first reaction given the following problem:
Calculate the enthalpy change for the reaction P4O6 + 2O2 -> P4O10 given the following enthalpies of reaction:
1) P4 + 3O2 -> P4O6 ∆H = -1640.1 kJ/mol
2) P4 + 5O2 -> P4O10 ∆H = -2940.1 kJ/mol
Flip the reaction and change the sign of ∆H
Which standard enthalpies of formations do you add together first when trying to find the standard enthalpy of a reaction?
products
Is CF4 a polar molecule?
No
Why can you add water to the top of a penny without the water spilling over?
The water adheres to itself with hydrogen bonds so it has surface tension that takes more energy to break.
What can you say about a reaction that has a ∆H=-87 kJ/mol?
it is exothermic
How does a catalyst affect a reaction? Relate this back to Hess' Law.
A catalyst lowers the activation energy, which changes the pathway of the reaction but does not affect the ∆H as per Hess' Law
What is the standard enthalpy of reaction for the following:
C4H8(g) --> 4C(s) + 4H2(g)
if ∆Hºf(C4H8) = -0.63 kJ/mol.
0.63 kJ/mol
Why is C2H8N nonpolar?
It is a symmetrical molecule.
What is the strongest IMF that could form between Ca2+ and CH4?
dispersion forces
Describe or draw an exothermic energy diagram. Label all parts.
Two axes labeled "energy" (y-axis) and "reaction coordinate" (x-axis). Energy of reactants on the left, relatively high up. A hump after the energy of reactants labeled at the top of the hump as "energy of transition state" and at the end as "energy of products" (this should be lower than the energy of reactants). The distance between the energy of reactants and the energy of transition state labelled "activation energy." The distance between the energy of reactants and the energy of the products labelled "∆H."
Where does the solution go WRONG in the following:
Example #1: Calculate the value of ΔH° for the following reaction:
P4O10(s) + 6PCl5(g) ---> 10Cl3PO(g)
using the following four equations:
(a) P4(s) + 6Cl2(g) ---> 4PCl3(g)ΔH° = −1225.6 kJ
(b) P4(s) + 5O2(g) ---> P4O10(s)ΔH° = −2967.3 kJ
(c) PCl3(g) + Cl2(g) ---> PCl5(g)ΔH° = −84.2 kJ
(d) PCl3(g) + 1⁄2O2(g) ---> Cl3PO(g)ΔH° = −285.7 kJ
Solution:
(a) P4(s) + 6Cl2(g) ---> 4PCl3(g)ΔH° = −1225.6 kJ
(b) P4O10(s) ---> P4(s) + 5O2(g)ΔH° = –2967.3 kJ
(c) 6PCl5(g) ---> 6PCl3(g) + 6Cl2(g)ΔH° = +505.2 kJ
(d) 10PCl3(g) + 5O2(g) ---> 10Cl3PO(g)ΔH° = −2857 kJ
6) The ΔH° values added together:
−1225.6 kJ + (–2967.3 kJ) + (+505.2 kJ) + (−2857 kJ) = −6544.7 kJ
7) The answer:
P4O10(s) + 6PCl5(g) ---> 10Cl3PO(g)ΔH° = −6544.7 kJ
What is the standard enthalpy of reaction for 4FeO(s) + O2(g) -> 2Fe2O3(s)?
-560.4 kJ/mol