Video: Applying Knowledge of the Flammability of H₂ Gas

For statements (I) and (II), state for each of they are true or false. (I) When a glowing splint is inserted into a sample of H₂ gas, surrounded by air, the H₂ ignites. (II) H₂ gas is flammable. If both are true, state if (II) is a correct explanation for (I).

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Video Transcript

For statements (I) and (II), state for each of they are true or false. (I) When a glowing splint is inserted into a sample of H2 gas, surrounded by air, the H2 ignites. (II) H2 gas is flammable. If both are true, state if (II) is a correct explanation for (I).

H2, hydrogen gas, and O2, oxygen gas, exist in the air together, along with other gasses, and do not normally react with each other under normal conditions. In other words, under normal temperature and pressure. These molecules move randomly through the air and, even if they do collide, will not react because they do not have enough kinetic energy to cause a reaction. But what happens in the case of increased kinetic energy?

When a glowing splint is inserted into a sample of hydrogen gas, surrounded by air, we know that oxygen is also present. The glowing splint supplies heat energy to the molecules. This heat energy is converted to an increase in kinetic energy in the molecules. And some of the molecules will have enough or sufficient kinetic energy to collide and undergo an effective collision. In an effective collision, we say there is sufficient activation energy. Activation energy is the energy required to cause bond breaking and bond formation.

The balanced equation for the reaction is 2H2 gas plus O2 gas, giving 2H2O gas. So, gaseous water molecules are formed after the reaction. A lot of energy in the form of heat, light, and sound is released as a result of this reaction. We say the H2 ignites or burns in the presence of oxygen. We would observe what looks like a mini explosion. We’ll hear a loud popping sound and a quick, bright flash of light.

Because of this release of energy, we say the reaction is exothermic. This is also an example of a combustion reaction because oxygen is one of the reactants and the reaction produces energy or releases energy. So, statement (I) when a glowing splint is inserted into a sample of H2 gas, surrounded by air, the H2 ignites. This is true. Statement (II) H2 gas is flammable is also true.

Note that in the lab to carry out this test, one would take a vessel full of H2 gas and invert it because H2 gas is less dense than air. Then insert the glowing splint into the bottom open mouth of the vessel. Here, oxygen from the air and the hydrogen gas can react with each other from the heat energy supplied by the glowing splint.

We have seen that both statements are true. And finally, we can say that statement (II) is a correct explanation for (I). It is because hydrogen gas is flammable that it can ignite in the presence of oxygen from the air and the heat supplied by glowing splint.

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