Honors General Chemistry 225H
Practice Midterm 1 100 pts total, 50 minutes.
NAME: _____KEY_______
Exams are closed book and notes, calculators are required. Obviously, no external communication devices
are allowed. A periodic table will be provided.
The universal gas constant, R, is 8.31 J/Kmol or 0.0821 Latm/Kmol
1)
1219 J of added heat raise the temperature of 250 g of a metal by 64°C. What is this metal’s
specific heat?
0.076 J / g°C
2)
What is the work done (in J) by the system when H2 expands against a constant pressure of 75
atm at 45.3 °C? The change in volume is 24.0 L. Is the sign of this energy change positive or
negative? (101 J = 1 L atm)
work = -1.8 × 105 J
3)
Determine the enthalpy change in the following reaction:
Cl2(g) + H2O(l) → 2 HCl(g) + 1/2 O2(g)
ΔHf° (H2O(l)) = -285.8 kJ/mol
ΔHf° (HCl(g)) = -92.31 kJ/mol
+101.2 kJ/mol
4)
Determine △Hrxn° for the following decomposition of hydrogen peroxide:
2 H2O2(l) →
O2(g) + 2 H2O(l)
given the following reaction enthalpies, in kJ/mol:
H2(g) + O2(g) → H2O2(l)
H2(g) + (1/2) O2(g) → H2O(l)
△H° = -187.8
△H° = -285.8
-196.0 kJ
5)
Circle the compound below with the lowest boiling point at 1.0 atm pressure. Explain your
reasoning.
CH4
SiH4
SiH2Cl2
SiCl4
GeH4
Lowest mass gives weakest vdw interactions. SiH2Cl2 is polar and will also have dipoledipole interactions.
6)
Given the data below, determine the normal boiling point of COCl2.
P1 = 100 mmHg, t1 = -35.6°C, ΔHvap = 27.4 kJ/mol
5.0 °C
7)
Sketch the phase diagram for CO2 and identify the position of the critical point, triple point, and
maximum temperature for sublimation. You do not need to put any values on your graph.
8)
Given the following information, calculate the lattice enthalpy for NaI(s):
ΔH° (kcal/mol)
Na(s) →
I2(g) →
I2(s)
→
I(g) + e- →
Na(g) →
2Na(s) + I2(s)
Na(g)
2I(g)
I2(g)
I-(g)
Na+(g) + e→ 2NaI(s)
+26
+36
+15
-71
+118
-699
448 kcal/mol
9)
Commercial perchloric acid is 70.0% by mass, HClO4(aq), and has a density of 1.67 g/mL.
Calculate the molarity of perchloric acid in the solution.
11.6 M
10)
Iron crystallizes in a body-centered cubic unit. The edge of this cell is 287 pm. Calculate the
density of iron in g/cm3. (Fe = 55.85 amu)
Density = Mass unit cell/ Volume unit cell
Mass unit cell = (2 atoms/cell) (55.85 g/mol) / 6.02E23 (1/mol)
Volume unit cell = a3 = (2.87E-8 cm)3
So density in g/cm3 = (2) (55.85) / (6.02E23) (2.87E-8)3
= 7.85 g/cm3
11)
Describe the structure of sodium chloride using capital letter for hexagonal 2D arrays and lowercase for cation 2D arrays. For example (AaBbCc)n refers to the sphalerite structure. Also, draw a
unit cell.
(AcBaCb)n