100 mL of PH3 when decomposed produces phosphorus and hydrogen. The change in volume is:
(a) 50 mL increase
(b) 500 mL decrease
(c) 900 mL decrease
(d) none of these
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(a) 2PH3(g) 2P(s) + 3H2(g)
100 0 0 Before dissociation
0 - 150 After dissociation
More explanation below:
As the volume occupied by gases only depends on number of moles of gases, the answer is related to number of moles of gases produced.
Since, no temperature and pressure is given, one can assume NTP.
At NTP, the reaction produces Phosphorous(Solid) and Hydrogen(gas). Looking at the balanced equation above, 2 moles of PH3 gas would give 3 moles of H2 gas.
Therefore, there is 50% increase in number of gaseous molecules after reaction. (2 to 3 moles)
As the volume depends on number of moles, the increased volume is also 50% more than original volume.
Increase in volume = Original Volume * 50 % = 100 ml * 50% = 50ml
New Volume = Original Volume + Increase in Volume = (100 + 50) ml = 150 ml