Chemistry
Chemistry
13th Edition
ISBN: 9781259911156
Author: Raymond Chang Dr., Jason Overby Professor
Publisher: McGraw-Hill Education
Question
Chapter 22, Problem 22.15QP
Interpretation Introduction

Interpretation:

Balanced equation for the reaction of CaH2 with H2O and grams CaH2 of needed for the formation of 26.4L of H2 has to be determined at 20oC and 746mmHg .

Concept introduction:

Balanced chemical equation

The mass of products should be equal to mass of its starting materials this is governed by law of conservation of mass.

Massofstartingmaterials(Reactants)=MassofproductsN2+H2NH3

In the above reaction 2 nitrogen atoms are there in reactant side but 1 nitrogen in product side, likewise 2 hydrogen’s in reactant side but 3 hydrogen’s in product side so this is unbalanced equation by putting coefficients for each elements in both sides we can balance this reaction as follows:

N2+3H22NH3

Expert Solution & Answer
Check Mark

Answer to Problem 22.15QP

  • Balanced equation for the reaction of CaH2 with H2O is given below:CaH2(s)+2H2O(l)Ca(OH)2(aq)+2H2(g)
  • The amount of CaH2 needed to produce 26.4L of H2 is 22.7 g

Explanation of Solution

The balanced equation for the given starting materials is given below:

CaH2(s)+2H2O(l)Ca(OH)2(aq)+2H2(g)

The reaction of calcium hydride with water gives calcium hydroxide and hydrogen gas as products. By putting coefficients of the starting materials and products the mass of starting materials will be equal to the mass of the products.

Pressure given as 746mmHg

Temperature given as 20oC

Gas constant value is 0.0821LatmKmol

Calculate the number of moles of H2

Ideal gas equation is given as follows,

PV=nRTP-pressure of gas; V-volume of gas; n-number of moles of gasR-Gas constant; T - temperature in Kelvin

Modify the ideal gas equation to calculate the number of moles of H2

n=PVRT

Substitute the values of P, V, R and T in the above equation

molH2=(746mmHg×1atm760mmHg)(26.4L)(0.0821LatmKmol)(293K)=(0.9816×26.40.0821×293)molH2=(25.914224.0553)molH2=1.077molH2

The number of moles of H2 is calculated as 1.007.

By using the modified ideal gas equation and given data the number of moles hydrogen was calculated as 1.007 moles.

By using the balanced equation calculate the amount of CaH2

CaH2(s)+2H2O(l)Ca(OH)2(aq)+2H2(g)

Two moles of H2 produced from one mole of CaH2.  So two moles of CaH2 is equivalent to one mole of H2

massofCaH2=molH2×1molCaH22molH2×molecularmassofCaH21molCaH2=1.077molH2×1molCaH22molH2×42.0939g1molCaH2=(1.077×0.5×42.0939)g=22.6676g

The mass of CaH2 needed to produce 26.4L of H2 is 22.6676 g.

By using the balanced chemical equation and the number of moles of hydrogen the amount of calcium hydride needed was calculated as 22.6676g.

Conclusion

Balanced equation and the mass of calcium hydride needed to produce the required amount of hydrogen gas were determined.

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Chapter 22 Solutions

Chemistry

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