Question

A loud classroom demonstration involves igniting a hydrogen-filled balloon. The hydrogen within the balloon reacts explosively with oxygen in the air to form water. If the balloon is filled with a mixture of hydrogen and oxygen, the explosion is even louder than if the balloon is filled only with hydrogen – the intensity of the explosion depends on the relative amounts of oxygen and hydrogen within the balloon. Draw the molecular views representing different amounts of hydrogen and oxygen in four different balloons. Write the balanced chemical equations for each of the four reactions. Using stoichiometry, discuss which balloon will make the loudest explosion and why.

Answer 1

When ignited, hydrogen gas combines with oxygen gas explosively in proportions ranging from 4.1 - 71.5% hydrogen - ignition temperature is 580 °C. The gaseous reaction is

2 H₂(g) + O₂(g) → 2 H₂O(g)

This exothermic reaction yields 232 kJ/mol of water formed. The rapid release of a considerable amount of energy causes the surrounding air to expand suddenly, resulting in a sharp expolsion. When pure hydrogen is ignited, the reaction with the surrounding air is less rapid, the sound is less loud, and a significantly larger flame is produced.

The amount of water produced directly influences the amount of heat produced and the amount of energy released. If the two gases are in the correct ratio of 1 oxygen to 2 hydrogen we get the loudest sound as the maximum amount of water is produced for the same volume of the balloon.

For any ration away from 1 oxygen to 2 hydrogen by volume and mole we will get a less louder sound. The farther we are away from this ratio the lesser amount of water is formed and thus lesser heat released and lesser sound.

To demonstrate les us take 4 balloons

Balloon A 1: 2 oxygen to hydrogen

Baloon B 1.2 : 1.8 oxygen and hydrogen

Balloon C 1:1 oxygen to hydrogen

Balloon 2:1 oxygen to hydrogen

So we will see A is the loudest followed by B, C and least loud is D.