Pop test

Last time I asked if you could write a symbol equation for the reaction between ammonia and hydrogen chloride gases.

The equation is:
NH3 (g) + HCl (g) –> NH4Cl (s)

I also asked why fluorescent inks in highlighter pens glow. The answer is that certain molecules within the ink absorb energy of one wavelengths (e.g. u.v.) and emit it at a longer wavelength, as visible light. Here are the inks extracted for the Halloween display in bright sunlight.

Highlighter pen inks in sunlight

Highlighter pen inks in sunlight


Finally, I also talked about a mixture of hydrogen and oxygen gases being unlikely to react until a spark or flame is introduced to the mixture. The spark or flame provides the necessary activation energy needed to get the reaction started between a few molecules, and then the two gases react explosively.

A small hydrogen and oxygen explosion

A small hydrogen and oxygen explosion

That this explosive reaction is exothermic is self evident. A lot of energy is given out as heat, light and sound. “Pop!”

Here are some .gif animations of hydrogen pop tests:

Hydrogen and oxygen bubbles ignited with a burning splint

Hydrogen and oxygen bubbles ignited with a burning splint

"Pop!" Testing hydrogen gas with a lighted splint.

“Pop!” Testing hydrogen gas with a lighted splint.

A value for the energy released (the enthalpy of reaction), can be calculated by using bond energies.
Calculating the enthalpy of combustion of hydrogen using bond energy values

Calculating the enthalpy of combustion of hydrogen using bond energy values

The bond energy calculation above uses the values listed in my September 29th blog.

However, this value is unlikely to be as accurate as the value obtained from direct calorimetry experiments.

Of course, it is possible for a mixture of hydrogen and oxygen gases to react spontaneously on its own, without a flame being supplied. It could happen if molecules of hydrogen and oxygen collided with enough energy (the activation energy) by chance. It is just rather unlikely at room temperature.

What is a B/Z reaction? And what does it show?