Part A Which of the following processes is exothermic? CO 2 (g) ? CO 2 (l) H 2 O
ID: 843242 • Letter: P
Question
Part A
Which of the following processes is exothermic?
CO2 (g) ? CO2 (l)
H2O (s) ? H2O (l)
Br2 (l) ? Br2 (g)
I2 (s) ? I2 (g)
C2H5OH (l) ? C2H5OH (g)
Part B
A particular system is doing work on the surroundings as well as gaining heat from the surroundings. What can be said about the values of q (heat) and w (work) for thie system?
q is positive and w is positive
q is negative and w is positive
nothing can be determined about q and w
q is positive and w is negative
q is negative and w is negative
Part C
The enthalpy change for the reaction A + 2B ? 3C can be determined using the following equations:
(1) 2 Z + C ? X ?H = 15 kJ
(2) 2 B + 3 X ? 3 Z ?H = 30 kJ
(3) 6 X ? A + 9 Z ?H = 20 kJ
Part D
To do this, which of the following changeshould be made to equation 2?
No changes should be made.
The equation should be flipped.
The equation should be flipped and multiplied by a factor of 3.
The equation should be multiplied by a factor of 3.
The equation should be multiplied by a factor of 1/3.
Part E
Consider:
2 B5H9 (g) + 12 O2 (g) ? 5 B2O3 (g) + 9 H2O (g) ?H?reaction= - 8687 kJ.
What is the enthalpy change when 0.2500 moles of B5H9 are combusted?
+1737 kJ
-2171 kJ
-1086 kJ
-6248 kJ
+1422 kJ
CO2 (g) ? CO2 (l)
H2O (s) ? H2O (l)
Br2 (l) ? Br2 (g)
I2 (s) ? I2 (g)
C2H5OH (l) ? C2H5OH (g)
Explanation / Answer
Part.A) CO2 (g) ==> CO2 (l)
Part.B) q is positive and w is negative
Part C)
2 Z + C ? X.............1) A + 9 Z ==>6X delH=-20kj.......a)
2 B + 3 X ? 3 Z................2) 2B+3X==>3Z delH=+30kj.........b)
6 X ? A + 9 Z....................3) 3X==>6Z+3C delH=-45kj.........c)
summing a, b and c gives A + 2B==>3C delH=-35kj
part D) No changes should be made to equation 2)
part E) -1086 kJ (i.e by dividing all the terms of equation by 8)