6.10 The Haber Process Flashcards
What is the haber process used for?
Making ammonia from hydrogen and nitrogen
How is the nitrogen in the haber process easily obtainable?
It can be easily obtained from the air, which is 78% nitrogen
Where does the hydrogen in the haber process come from?
The hydrogen mainly comes from reacting methane (from natural gas) with steam to form hydrogen and carbon dioxide
In the haber process, what type of catalyst are the reactant gases passed over?
An iron catalyst
What temperature is used in the haber process?
450 degrees celsius
What pressure is used in the haber process?
200 atmospheres
Why is it significant that it is a reversible reaction?
In the reaction vessel, there will still be hydrogen and nitrogen as some of the ammonia produced converts back into hydrogen and nitrogen again. This means that we will need to separate them from the ammonia we need
How does the nitrogen, hydrogen and ammonia separate from each other in order to get liquid ammonia?
As ammonia has a fairly low boiling point, as it passes through to the condenser (which is much colder than the reaction vessel) the gaseous ammonia is cooled down until it condenses into liquid ammonia. The gaseous hydrogen and gaseous nitrogen will remain a gas as they have a lower boiling point and so they can be recycled back around into our reaction mixture.
Why is 450 degrees celsius used for the haber process?
The reaction in the haber process is exothermic. That means that increasing the temperature will move the equilibrium the wrong way - away from ammonia and towards nitrogen and hydrogen. So the yield of ammonia would be greater at lower temperatures. Trouble is, lower temperatures mean a slower rate of reaction as more kinetic energy means a higher rate of reaction. The 450 degrees is a compromise between maximum yield and speed of reaction. Also, generating heat is expensive; using a higher temperature would be too costly.
Why is 200 atm of pressure used in the haber process?
To achieve a higher % yield, we need a high pressure as higher pressures move the position of equilibrium towards the products since there are four molecules of gas on the left-hand side for every two molecules on the right. It also increases rate of reaction as higher pressures mean the particles collide more frequently and so can react more. Both of the points indicate that we need a high pressure so the only thing limiting how high we make the pressure is the practical considerations like cost or safety. The pressure is set as high as possible, without making the process too expensive or dangerous to build and maintain.
Why is the iron catalyst in the haber process used?
The iron catalyst makes the reaction go faster, but doesn’t affect the yield. This means it’s possible to get an acceptable rate without raising the temperature or pressure to undesirable levels.
What is the word equation for the reaction of the Haber process?
nitrogen + hydrogen —> ammonia
Why is ammonia so important?
It is used in fertilisers
