Gases, reversible reactions and ammonia - C3.4 Heba Saey

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Transcript of Gases, reversible reactions and ammonia - C3.4 Heba Saey

  • 1. Gases, Reversible reactions and Ammonia C3.4 Love, Heba

2. Calculating Volumes 3. Important fact- ( AVOGADROS LAW) get this stuck in your head! One mole of any gas always occupies at room temperature and atmospheric pressure. In other words One mole of anyyyyy Gas even one mole of fart gas will always have a volume of at room temperature which is usually 25 degrees, and 1 atmosphere! ( got it?) I REMEMBER HIS NAME BY : AVOCADOS LAW ( OBV DONTWRITE THAT INTHE EXAM) 4. Volumes of Gases 2 formulas Moles in Volumes of Gases Volume Moles 24 Volume of Gas = = x 24 Dont worry.. It will make sense in the next few slides 5. Note When dealing with Calculating Volumes questions , you need to realise That you may be required to know the following: - Calculating Masses ( like in C2) - Use the Mass/ Mr = no. of moles 6. Example 1 Whats the volume of 4.5 moles of chlorine at RTP ( ROOM TEMP) Volume Moles 24 Step 1) Know which formula your using Step 2) Volume = moles x 24 Step 3) Moles given = 4.5 Step 4 ) 4.5 x 24 = volume Step 5 ) Answer = 108 Volume = 3 7. Example 2 How many moles are there in 8280 3 of hydrogen Gas? ( beware look at the volume) Volume Moles 24 Step 1) Know which formula your using Step 2) Moles = volume/24 Step 3) Volume given = 8280/1000= 8.28 Step 4 ) 8.28/24= moles Step 5 ) Answer = 0.345 moles Volume = 3 8. Volumes in reactions ( dont freak out! ) = x 24 Two stages 1) Find reacting mass ( like in C2 ) 2) Convert mass into volume using formula below Example : Find the Volume of Carbon dioxide produced at RTP when 2.7g of carbon is completely burned in oxygen. To do this : 1) Find the reacting mass of carbon dioxide 2) Use the formula on the side ( ill show you on the next slide) 9. Example 1 Example : Find the Volume of Carbon dioxide produced at RTP when 2.7g of carbon is completely burned in oxygen. FIRSTLY : Write balanced equation: + 2 2 Only use what's required in this case we only need Carbon and Carbon dioxide NOT Oxygen. C 2 Mr / Ar 12 12+ ( 16 x 2) = 44 Divide by 12 1 3.666666 Multiply by 2.7 g 2.7g 9.9 g So 2.7 g of Carbon gives you 9.9 g ( got it ? ) = x 24 Volume of Carbon dioxide = 9.9 44 x 24 ANSWER : 5.40 3 10. Example 2 ( using Moles and Volumes ) Example How much carbon dioxide is formed when 30 3 of Oxygen reacts with carbon monoxide? FIRSTLY : Write balanced equation: 2 + 2 22 Only use what's required in this case we only need Oxygen and Carbon dioxide NOT Carbon monoxide. 2 22 How many moles in reaction? 1 2 Volume ( always equal to no. of moles in equation ) 1 2 Volume in reaction 30 3 2 x 30 3= 603 So 303 of Oxygen gives you 603 of Carbon dioxide ( got it ? ) = x 24 11. Reversible Reactions 12. Basics about reversible reactions A Reversible reaction is one where the products of the reaction can react together and convert back to the original reactants ( in other words it can go both ways) + + 13. All reversible reactions will reach a Dynamic Equilibrium .. DYNAMIC EQUILBRIUM Reactions in a closed system ( where no reactants can escape ) always reach a state of equilibrium. Equilibrium basically means that the amounts of reactant and products will reach a certain balance and stay there.. Happening in both directions, but the overall effect is nil. This is because the forward and reverse reactions cancel each other out b/c their Happening at exactly the same rate in both directions. ( DONT confuse yourself by visualising it..JUST LEARN IT ) 14. Effect of temperature on an equilibrium Remember Endothermic and Exothermic? If more energy in the form of heat is required to break old bonds then the reaction is endothermic. If less energy in the form of heat is required to break old bonds, but new bond forming produces more heat energy this is exothermic.. + HEAT ENDOTHERMIC EXOTHERMIC+ + 15. FORWARD ( RIGHT) REACTION = EXOTHERMIC BACKWARD ( LEFT ) REACTION = ENDOTHERMIC MORE VOLUME = LEFT LESS VOLUME = RIGHT ( this will make sense later ) 16. What if we raised the temperature? ENDOTHERMIC reaction will be favoured What the F**K does that mean??? ( CGP ARE SHIT AT EXPLAINING SOMETIMES) Remember how we said that when old bonds are broken, if they use a lot of energy in the form of heat , then the reaction is endothermic. Therefore, if we raise the temperature, the reaction will use up the extra heat to break old bonds. So therefore the position of equilibrium will be towards the left because the products on the right are broken into the two reactants HEAT is required to do this This reduces the amount of product produced 17. What if we reduced the temperature? EXOTHERMIC reaction will be favoured What the F**K does that mean??? ( CGP ARE SHIT AT EXPLAINING SOMETIMES) Exothermic produce heat when new bonds are formed. They require much less Heat energy to form these new bonds, therefore if the temperature is lowered, the bond forming part of the reaction ( usually to the right) will be favoured.. DUH! Usually this would be the products section of the equation. So if there is a reduce in temperature, the amount of products produced will increase. Still confused.. There's a picture on the next slide 18. Endothermic reaction Will result in producing These two reactants as bonds are broken - Raising temperat ure will lead to equilibria moving To the left ( less product) Exothermic Reaction would produce a product ( new bonds ) and will also produce heat. Less heat is required for this process to occur. So lowering the temperature wouldn't bother the exothermic section of the reaction 19. Pressure and position of Equilibrium To start off with You need to know how to know which side has the most volume N2(g) + 3H2(g) 2NH3(g) 1+3 = 4 2HIGHER VOLUME 20. What if we raise the pressure? From the previous slide, we realised that there is more volume on the left side of the reaction compared to the right If we increase the pressure OBVIOUSLY the side making less volume will be favoured, this will help make MORE volume. The side with the less volume is favoured as it has much less pressure/volume. 21. What if we reduce the pressure? From the previous slide, we realised that there is more volume on the left side of the reaction compared to the right If we decrease the pressure OBVIOUSLY the side making more volume will be favoured, this will reduce the volume produced . The side with the more volume is favoured as it has much more pressure/volume. 22. The whole reason for the differences in equilibrium position is to maintain a balanced reaction overall and to reach equilibrium . 23. Catalyst effects Increasing temperature and pressure will only increase the rate of reaction and so you reach equilibrium faster. However it will result in less product being made The catalyst does not affect the yield, but it does increase the rate of the reaction. This allows a lower temperature to be used (increasing temperature is one way of speeding up a reaction) and using a lower temperature allows the yield to be maximised as well as saving money on energy costs. 24. To wrap up Look at the graph. You can see that for any given temperature the yield of ammonia increases as the pressure increases. You can also see that, for any given pressure, the yield goes down as the temperature increases. This is because the forward reaction is exothermic. 25. The Haber process 26. This process produces AMMONIA N2(g) + 3H2(g) 2NH3(g) Nitrogen extracted from air Hydrogen- obtained from natural gas This is a reversible reaction , occurring in both directions, not all the hydrogen and nitrogen will be converted to ammonia. The reaction reaches dynamic equilibrium where the amount of reactants will be balanced with the amount of product produced. 27. Conditions required in industry to manufacture Ammonia: Pressure : 200 atmospheres Temperature : 400c Catalyst : Iron 28. The process not as hard as you think - High pressure is used as the forward reaction is favoured- therefore pressure is set high as possible to produce the highest % yield of ammonia - The forward reaction is exothermic ( reducing temp = increase yield) , however you must remember that the high temperature supplied in this process causes equilibrium to move the wrong way towards the backward reaction. - We know lower temperatures produce higher yields , but its very slow, so they increase the temperature anyways to get a much faster rate of reaction - 450 degrees would produce less yield than in lower temperature, but its best to gain yield at a faster rate - Ammonia is formed as gas , but as it cools in the condenser it liquefies and is removed - Iron catalyst makes reaction go faster, but remember it doesnt affect the %yield 29. High pressure favours 2NH3 causing higher % yield of 2NH3 N2(g) + 3H2(g) 2NH3(g) 1+3 = 4 2HIGHER VOLUME 30. In summary . . . High temperatures makes reaction reach equilibrium quicker. The reason why low temperatures aren't used is because its slower despite it producing more. The temp used still produces yield because temp is moderately high. High pressure is used as it favours the forward reaction ( the one with less volume) , causing a higher yield Iron catalyst speeds up reaction but doesnt affect position of equilibrium. 31. Uses and disadvantages of Ammonia Uses Disadvantages ( eutrophication) Used to manufacture Nitrogenous fertilisers used to Increase plant growth Fertilisers stimulate excessive growth of algae on surface of water Plants living below the surface die because the algae blocks the light- they cant photosynthesise Decomposers feed on dead plants they use up oxygen, causing fish to die DID THIS IN B1