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Contract or Expanding Gases

1. A sample of N2 gas occupies 2.40 L at 20oC. If the gas is in a container that can contract or expand at constant pressure, at what temperature will the N2 occupy 4.80 L?

10oC
40oC
146oC
313oC
685oC

2. When 0.56 g of Na(s) reacts with excess F2(g) to form NaF(s), 13.8 kJ of heat is evolved at standard-state conditions. What is the standard enthalpy of formation (ΔH) of NaF(s)?

+24.8 kJ/mol
+570 kJ/mol
-24.8 kJ/mol
-7.8 kJ/mol
-570 kJ/mol

3. Given:

H2(g) + ½O2(g) H2O(l), ΔH = -286 kJ

What is the enthalpy change for the following reaction?

2H2O(l) 2H2(g) + O2(g), ΔHorxn = ?

ΔHo = -286 kJ
ΔHo = +286 kJ
ΔHo = -572 kJ
ΔHo = +572 kJ
ΔHo = -143 kJ

Solution Preview

A sample of N2 gas occupies 2.40 L at 20oC. If the gas is in a container that can contract or expand at constant pressure, at what temperature will the N2 occupy 4.80 L?

10oC
40oC
146oC
313oC
685oC
Solution
The above problem is based on Charles law, as pressure is constant throughout the experiment.

Data given are
V1 = 2.40L
T1=20 + 273 = 293 K
V2 = 4.80 L
T2 =?

T2 = 586 K or 313°C

2. When 0.56 g of Na(s) reacts with excess F2(g) to form NaF(s), 13.8 kJ of heat is evolved at ...

Solution Summary

Contracting and expanding gases at different temperatures are examined.

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