Conceptual Questions
At the same temperature, which has the higher average speed: H₂ or O₂? Why?
H₂ has a higher average speed because lighter molecules move faster at the same temperature
A reaction produces 0.75 mol of hydrogen gas. What volume will it occupy at 1 atm and 273 K?
Which of the following are state functions: q, w, H, E, T, P?
H, E, T, P
Under what conditions do gases behave non-ideally?
High pressure and low temperature
A scuba tank initially at 12 L and 3.0 atm is compressed to 8.0 L at a constant temperature of 35 C
Calculate ΔH°rxn for:
2NO(g)+O2(g)→2NO2(g)
Given ΔHf:
NO(g) = +90.3 kJ/mol
NO₂(g) = +33.2 kJ/mol
O₂(g) = 0
-114.2 kJ
What are some of the Kinetic Molecular Theory Postulates?
And which law is it the foundation of?
Gas particles are in constant, random motion.
Gas particles have negligible volume compared to the container.
Collisions between particles and with container walls are elastic (no energy lost).
There are no intermolecular forces between particles.
Average kinetic energy of gas particles is proportional to temperature (in Kelvin).
A mixture contains nitrogen and carbon dioxide. If total pressure is 780 torr and nitrogen exerts 620 torr, what is carbon dioxide’s pressure?
Dalton's Law of Partial Pressure
Use the following enthalpy changes
KClO3(s) + 3Mg(s) → KClO3(s) + 3MgO(s) ΔH = –1852 kJ mol–1
K(s) + ½Cl2(g) → KCl(s) ΔH = –437 kJ mol–1
Mg(s) + ½O2(g) → MgO(s) ΔH = –602 kJ mol–1
to calculate the enthalpy change in kJ mol-1, for the reaction:
K(s) + ½Cl2(g) + 1½O2(g) → KClO3(s)
-391 kJ
How do you find partial pressure of gases when given total pressure and mol of each gas?
Use mol fraction, then multiply fraction by total pressure
A gas occupies 3.0 L at 1.2 atm and 300 K; what will the volume be at 0.8 atm and 330 K?
What is a standard formation reaction, and how would you write the standard formation reaction for liquid water H₂O(l)
A standard formation reaction makes 1 mole of a compound from its elements in their standard states
1/2 O2(g)+H2(g)→H2O(l)
What do the a and b terms represent in the van der Waals equation?
a corrects for intermolecular attractions, reducing observed pressure.
b corrects for finite molecular volume, reducing free volume available for motion
A balloon expands from 1.5 L at 25 °C to 1.62 L at 35 °C at constant pressure.
Charles's Law
Calorimeters such as coffee cups are at constant ___________
Calorimeters such as bomb calorimeters are at constant ___________
What thermodynamic quantity does each one measure?
Coffee cup: pressure --> H (enthalpy change)
Bomb: volume --> E (internal energy change)