1. Calcium hydride, CaH2, reacts with water to form hydrogen gas: CaH21s2+2 H2O1
ID: 1041497 • Letter: 1
Question
1. Calcium hydride, CaH2, reacts with water to form hydrogen gas: CaH21s2+2 H2O1l2¡Ca1OH221aq2+2 H21g2 This reaction is sometimes used to inflate life rafts, weather balloons, and the like, when a simple, compact means of generating H2 is desired. How many grams of CaH2 are needed to generate 145 L of H2 gas if the pressure of H2 is 825 torr at 21 °C?
2. Indicate which of the following statements regarding the kinetic-molecular theory of gases are correct. (a) The average kinetic energy of a collection of gas molecules at a given tem-perature is proportional to m1>2. (b) The gas molecules are as-sumed to exert no forces on each other. (c) All the molecules of a gas at a given temperature have the same kinetic energy. (d) The volume of the gas molecules is negligible in compari-son to the total volume in which the gas is contained. (e) All gas molecules move with the same speed if they are at the same temperature.
Explanation / Answer
Answer 1
From the above equation it is clear that , 1 mol of calcium hydride will liberate 2 mol of hydrogen gas
So, no. of moles of H2 gas required if if the pressure of H2 is 825 torr at 21 °C =
Assuming ideal condition,
P*V = n*R*T, where n = no.of moles
n= (p* V)/(R*T)
(1.08553 atm * 145 l)/(0.0821 atm L mol-1 K-1 * 294 K) [760 Torr = 1 atm]
= 6.52 moles
To liberate 6.52 moles hydrogen gas , 3.26 moles of calcium hydide is recquired
1 mole of calcium hydrate contains 42.094 gm
Thus 3.26 mole will contain 137.226 gm
137.226 g of CaH2 are needed to generate 145 L of H2 gas if the pressure of H2 is 825 torr at 21 °C.
Answer 2
Statements b, c and d are correct
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