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N-9
Percent error =
experimental value - accepted value
accepted value
x 100%
ADVANCE STUDY ASSIGNMENT
1.
What condition allows you to determine ?H values using the procedure described in this
experiment?
Answer: Reactions are done at constant pressure.
2.
What is an exothermic reaction? What is an endothermic reaction?
3.
How is the amount of heat absorbed by the water in a calorimeter related to the heat released
by the reaction (q
sys
)?
Answer: q
sys
= -q
surr
= -q
(absorbed /released by water)
4.
The accepted heat of formation of liquid water is -285.8 kJ/mol. Does the reaction
H
2(g)
+
1
2
O
2(g)
H2O
(l)
give off or absorb heat? If you experimentally determine this heat of formation as -271
kJ/mol, what is your percent error? Answer: 5.2 %
5.
The dissolution of NaNO
2(s)
in water is endothermic. What happens to the temperature of the
water as NaNO
2(s)
dissolves? Sketch a graph of the temperature of the water against time as
the reaction proceeds.
6.
A 0.582 g sample of magnesium reacts with excess 1.0 M HCl (60.0 mL) according to the
procedure used in this experiment. The initial and extrapolated temperatures are 24.0 °C
and 68.3 °C respectively. What is the ?H of the reaction per mole of magnesium? Use the
correct number of significant figures, and give units. Assume all heat is absorbed by the
water. Water has a specific heat capacity of 4.184 J/g
C and density of 1.00 g/mL. Answer: -469 kJ/mol
REAGENTS AND EQUIPMENT
two Styrofoam cups and one lid
1.0 M hydrochloric acid (HCl)
thermometers
- standard
magnesium powder (Mg)
- 0.1°C divisions
magnesium oxide (MgO)
rubber elastic
sodium sulfate decahydrate (Na2SO
4
•10 H2O)
