“When set on fire, Hydrogen reacts with nearby air containing oxygen to release a large amount of heat . The release of such heat causes a mini explosion and gives a pop sound’’.
The question is an interesting one to know about , but have you ever thought about the following questions :
What causes the pop sounds ?
What is the chemistry behind burning hydrogen ?
Why is a mixture of hydrogen with air or oxygen in closed containers or balloons dangerous ?
Why is Helium used instead of Hydrogen in balloons ?
There are many more facts to think about which we shall be unfolding in the next few paragraphs.
What does “Set on Fire ” exactly mean ?
For any substance to be set on fire or in common language - burn ,
Three main conditions are required :
a) Substance to be burn
b) Ignition Temperature
c) Oxidizing Medium( Oxygen)
PicCredit : wright.nasa.gov
In our case , hydrogen is the substance to be set on fire or burnt.
Every substance has a particular temperature above which it reacts with air and undergoes combustion . This temperature is known as ignition temperature.
It may be high for metals like 1315 ⁰C for Iron and 35 ⁰C for red phosphorus. For hydrogen, it is 585 ⁰C. which means if a test tube containing a mixture of air and hydrogen is heated to a temperature of 585 ⁰C , then it will react and undergo combustion.
PicCredit : physicscatalyst.com
We are constantly talking about air/oxygen and hydrogen mixture for combustion.
In every combustion process ,oxygen present in air reacts with the substance to be burnt to set the fire or combustion.
If we cannot ensure proper supply of oxygen ,the combustion process will not proceed.
At the furnace or oven , everyone of you would have noticed that we blow air towards the burning substance . When burning, every substance produces gases or smoke .These smokes are nothing but oxides of that material ( like CO₂ or CO while burning coal) .These gases act as a blanket on the material burning and stop the inflow of fresh oxygen or air. So, we blow air to remove these gases which act as a blanket and provide a path for fresh supply of oxygen.
Now , we have covered the basic principle of combustion . Now , we shall be learning about the combustion process of hydrogen .
How does Hydrogen Burn ?
Before moving forward , Think about :
Why do we get heat when we feel cool when sweat is evaporated from our body surface and feel hot during combustion of any fuel like coal ?
During hydrogen burning , hydrogen reacts with oxygen present in air when heated up to 585⁰ C (ignition temperature) and sets on fire. This reaction is an exothermic process which means heat energy is released during the process .On the other hand, evaporation of water absorbs heat from the surface and lowers the temperature. Such a process is called an endothermic process.
Hydrogen and oxygen molecules react and form water along with heat energy.
PicCredit :flexbooks.ck.org
Water is an oxide of hydrogen which is produced on combustion of hydrogen just like CO₂ which is produced on combustion of carbon/coal.
Water and CO₂ both are oxides which cannot be burnt any further in normal conditions and act as a blanket to prevent fresh air. So ,they are used as fire-extinguishing mediums.
Hydrogen has the highest calorific value which means it releases a large amount of heat during the combustion process. It is a highly flammable gas as it can catch fire easily.
Pic Credit : researchgate.net
Now comes the main question :
Why does Hydrogen Pop when set on fire ?
In the last segment, we get to know that a large amount of heat is released when hydrogen is set on fire.
This heat energy increases the temperature of gases and the molecules in particles start moving faster because the kinetic energy of gases increases with increase in temperature of gas. This fast movement causes large expansion of gas in very less or almost negligible amount of time. The molecules fastly try to move out of the test tube and collide with each other causing a mini collision breaking the sound barrier. The pop sound comes as a result of this mini- collision .
PicCredit: lebanon-express.com
It should be interesting to note that this pop sound comes out when hydrogen is set on fire in a test tube because the heated gas molecules suddenly expands and gets insufficient space due to which they try to come out of the small mouth of the tube causing an explosion .
Pic Credit : teleskola.mt
On the other hand, if hydrogen is heated in open air , the heated molecules will have all directions to move outwards and does not cause a high pressure zone as in case of tube. The molecules will get sufficient space to expand due to which collision or explosion does not take place .
Applications :
So far we have learnt about the underlying principle and process involved in Hydrogen popping when set on fire.
Now ,try to think of a few applications of this article in practical life .
Presence of hydrogen gas is detected by burning a candle near the hydrogen source like reaction of a metal (Mg) with an acid (HCl) . A popping sound will indicate the presence of hydrogen.
PicCredit : nygh.sg
Helium is used in place of hydrogen in gas balloons because Helium is inert gas and does not react with air to cause explosion .
Even while filling hydrogen , we prevent air entering the balloon because air consists of oxygen and can become an oxidizing medium for hydrogen. Without presence of oxygen, burning cannot take place.
No comments:
Post a Comment
Anyone having any query,suggestions or advice,please let me know.