Values for the molar mass of hydrogen, oxygen, and water molecules are given in the table below. What mass of water is formed when 2 moles of hydrogen react with 1 mole of oxygen to form water?

number of moles × molar mass of hydrogen + number of moles × molar mass of oxygen = water mass

Solution:

The two equation given which are in two variables are

1. y = x²-2 x -1 9

2. y + 4 x=5

Writing equation 2 as→y = 5 -4 x

Substituting the value of y in equation 1

⇒ 5 - 4 x = x² - 2 x - 19

⇒x² - 2 x + 4 x -19 -5=0

⇒ x² + 2 x -24=0

⇒x² + 6 x - 4 x - 24=0→→→[Breaking the middle term i.e term containing x]

⇒ x(x+6) -4(x+6)=0

⇒(x-4)(x+6)=0

⇒x-4=0 ∧ x+6=0

⇒x = 4     ∧    x= -6

Put x=4 in equation 2,

y + 4 ×4=5

y + 16=5

y = 5-16

y= -11

As one solution is (-6, 29), The other solution of the system of equation is (4, -11).