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# C3 Haber and gases

Describe the environmental problems caused by using too much fertiliser washed into rivers/leached from soil (1) algal blooms in lakes (1) microorganisms use up oxygen when
decomposing this material (1) death of other organisms in the water (1)
What is meant by the term dynamic equilibrium? both (forward and back) reactions occur at same time (1) at same rate (1)
A factory makes 100 moles of ammonia gas. What volume would this gas occupy at room temperature and pressure? 1mole occupies 24dm3 so 100 moles would occupy 2400dm3
In the manufacture of ammonia, NH3, a pressure of 200 atm is used. Using a higher pressure would mean that more ammonia would be formed at equilibrium. Give two reasons why a higher pressure is not used in industry? uses more energy (1) requires more powerful pumps (1) thicker-walled pipes needed (1) risk of explosion (1)
The forward reaction producing ammonia is exothermic. Explain what would happen to the yield of ammonia at equilibrium if the temperature was increased. use model answer “system will counteract change by decreasing the temperature; we know that forward is exo so equilibrium moves to left-hand side/endothermic direction (1) and yield will decrease
Hydrogen reacts with nitrogen to produce ammonia. 3H2(g) + N2(g)  2NH3(g) Give the meaning of  in the equation reversible reaction/reaction goes both ways
3H2(g) + N2(g)  2NH3(g) What is the minimum volume of hydrogen needed to react completely with 300 cm3 of nitrogen? because it is gas to gas reaction, we simply need to look at the ratio 3 H2:1 N2 so 3 times as much Hydrogen ie 900cm3
1 mol of magnesium, Mg, reacts to give 1 mol of hydrogen, H2. The experiment shows that 0.072 g of magnesium reacts to produce 66 cm3 of hydrogen. Calculate the volume of 1 mol of hydrogen, H2 (relative atomic mass: Mg = 24) this is a mass to volume so sucue; moles Mg = 0.072/24=0.0030; moles H2=moles Mg; volume =66/0.003=22 000 cm3; note that HERE we can NOT assume that volume is 24000cm3
When the experiment was repeated (Mg placed in acid), the volume of 1 mol of hydrogen, H2, was found to be 23000 cm3. The molar volume of hydrogen is 24000 cm3 at room temperature and atmospheric pressure. Suggest why these volumes are different temperature lower/pressure
higher/ some hydrogen escapes (1) hence calculated volume lower (1)
Calcium reacts with water to produce hydrogen. Ca + 2H2O → Ca(OH)2 + H2 Calculate the volume of H2, that could be produced from 15 g of calcium. ( Ca = 40, 1 mol of hydrogen, H2, occupies 24000 cm3 at room temperature and atmospheric pressure) this is a mass to volume so sucue; moles Ca = 15/40= 0.375; molesH2=moles Ca;volume H2 = 15 x 24000(1) = 9000 cm3
N2(g) + 3H2(g)  2NH3(g). The pressure used in industry is 250 atmospheres. Explain how the use of a higher pressure would affect the equilibrium yield of ammonia. use model answer “system will counteract change by decreasing the pressure; we know that there are less moles on right so equilibrium moves to right and yield will increase
The reaction between nitrogen and hydrogen to form ammonia is exothermic. The temperature used in industry is 450°C. Explain how the use of a lower temperature would affect the equilibrium yield of ammonia. use model answer “system will counteract change by increasing the temperature; we know that forward is exo so equilibrium moves to right-hand side/exothermic direction (1) and yield will increase
Even at 450C, the reaction between nitrogen and hydrogen to form ammonia is very slow. State what is used in industry to overcome this problem. use an (iron) catalyst
N2(g) + 3H2(g)  2NH3(g). Calculate the minimum volume of hydrogen required to completely convert 1000 dm3 of nitrogen into ammonia. because it is gas to gas reaction, we simply need to look at the ratio 3 H2:1 N2 so 3 times as much Hydrogen ie 3000dm3
Ammonia is reacted with excess nitric acid, HNO3, to make ammonium nitrate, NH4NO3. NH3 + HNO3 → NH4NO3 Calculate the mass of ammonium nitrate produced by the reaction of 34 g of ammonia. (Relative atomic masses H = 1.0, N = 14, O = 16) this is a mass to volume so sucue; RFM (NH4NO3)=80; RFM(NH3)=17; moles NH3=34/17=2; moles NH4NO3 = moles NH3; mass NH4NO3=molesxRFM=2x80=160g
Hydrogen reacts with oxygen to form water vapour. 2H2(g) + O2(g)  2H2O(g) If 200 cm3 of hydrogen react completely with 100 cm3 of oxygen, what is the maximum volume of water vapour formed, if all volumes are measured at the same temperature and pressure? because it is gas to gas reaction, we simply need to look at the ratio 2 H2:2 H2O so same volume of H2 and H2O ie 200dm3
Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) Calculate the volume of hydrogen formed, when 13.0 g of zinc reacts completely with excess hydrochloric acid. (relative atomic mass: Zn = 65.0, 1 mol of any gas occupies 24 dm3 at room temperature and pressure) this is a mass to volume so sucue;moles Zn=13/65=0.2; moles H2=moles Zn; vol H2=molesx24=4.8dm3
What is the source of the hydrogen used in the Haber process? Natural gas (although in the future we may use electrolysis of water)
What is the source of the nitrogen used in the Haber process? Air
When nitrogen reacts with hydrogen, the amount of ammonia gradually increases until it becomes constant. N2(g) + 3H2(g)  2NH3(g) Explain why the amount of ammonia remains constant. the rate of the forward reaction is the same as the rate of the backward reaction
N2(g) + 3H2(g)  2NH3(g) Calculate the minimum volume of nitrogen, in dm3, required to react completely with 1000 dm3 of hydrogen. All volumes are measured at the same temperature and pressure. because it is gas to gas reaction, we simply need to look at the ratio 3 H2:1 N2 so 3 times as much Hydrogen ie 333dm3 of Nitrogen needed
The minimum volumes of nitrogen and hydrogen that must react completely to form 5000 dm3 of ammonia are mixed and left, under appropriate conditions, until equilibrium reached. Explain which gas or gases will be present when equilibrium is reached All three gases!!! At equilibrium you have a mixture of reactants and products
N2(g) + 3H2(g)  2NH3(g) Explain the effect on the equilibrium yield of ammonia, when the Haber process is carried out at a pressure higher than 200 atm YIELD=SHIFT; use model answer “system will counteract change by decreasing the pressure; we know that forward is exo so equilibrium moves to right-hand side/exothermic direction (1) and yield will increase
N2(g) + 3H2(g)  2NH3(g) Explain the effect on the rate of attainment of equilibrium, when the process is carried out at a pressure higher than 200 atm increased pressure=more frequent collisions=higher rate (remember to answer the question: do not only say “faster reaction”)
Created by: UrsulineChem