12. Nitrogen and sulfur
A section of Chemistry, 9701
Listing 10 of 350 questions
Nitrogenmonoxide, NO, reacts with oxygen to form nitrogendioxide, NO2. 2NO+ O22NO2The rate equation for the forward reaction is shown. rate = k2 Complete the following table. the order of reaction with respect to the order of reaction with respect to the overall order of reaction  Two separate experiments are carried out at 30 °C to determine the rate of the forward reaction. experiment / mol dm–3 / mol dm–3 rate / mol dm–3 s–1 0.00300 0.00200 1.51 × 10–4 0.00500 6.05 × 10–5 Use the data for experiment1 to calculate the value of the rate constant, k. State the units of k.  k = units =  Calculate the value of in experiment2.  = mol dm–3 Define the term rate-determining step. Peroxodisulfate ions, S2O8 2–, react with iodide ions, I–. S2O8 2– + 2I– → 2SO4 2– + I2 The rate equation for the reaction in the absence of any catalyst is shown. rate = k[S2O8 2–][I–] Suggest equations for a two-step mechanism for this reaction, stating which of the two steps is the rate-determining step. step 1 step 2 rate-determining step =  A large excess of peroxodisulfate ions is mixed with iodide ions. Immediately after mixing, [I–]=0.00780 mol dm–3. Under the conditions used, the half-life of [I–] is 48seconds. Calculate the iodide ion concentration 192seconds after the peroxodisulfate and iodide ions are mixed.  iodide ion concentration = mol dm–3 
9701_w20_qp_43
THEORY
2020
Paper 4, Variant 3
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NO and NO2 react at 25 °C to give N2O3 as shown in the equation. NO+ NO2N2O3ΔH = –7.2 kJ mol–1 The reaction is reversible and reaches equilibrium in a closed system. shows how the rate of the forward reaction changes with time. Initially, the rate of the reverse reaction is zero. Complete to sketch how the rate of the reverse reaction changes with time. rate of reaction time State how the position of equilibrium changes, if at all, when the reaction takes place at 100 °C. Explain your answer. Assume the pressure remains constant. Table 2.1 shows the composition of an equilibrium mixture of NO, NO2and N2O3at 101 kPa. Table 2.1 gas number of moles at equilibrium / mol NO 0.605 NO2 0.605 N2O3 0.390 Calculate Kp , the equilibrium constant with respect to partial pressures. Deduce the units of Kp. Kp = units Identify one natural process and one man-made process that cause the formation of atmospheric NO and NO2. natural process man-made process NO2 is a brown gas that can be used to form nitric acid. NO2 is a free radical. Define free radical. NO2 has a catalytic role in the oxidation of atmospheric sulfur dioxide. Write equations to show the catalytic role of NO2 in this oxidation. State one environmental consequence of the oxidation of atmospheric sulfur dioxide. A student titrates nitric acid with a base to form a solution containing aqueous magnesium nitrate. Identify a base that the student could use. The student evaporates the water to obtain magnesium nitrate solid. When this solid is heated it decomposes. Write an equation for the decomposition of magnesium nitrate. State how the thermal stability of Group 2 nitrates changes down the group.
9701_w23_qp_22
THEORY
2023
Paper 2, Variant 2
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Nitrogen dioxide, NO2, can enter the atmosphere in a variety of ways. State one natural and one man-made source of atmospheric NO2. natural man-made Write an equation to show how NO2 leads to the formation of nitric acid in acid rain. Use equations to illustrate the catalytic role of NO2 in the formation of sulfuric acid in acid rain. Nitrogen dioxide exists in equilibrium with dinitrogen tetroxide, N2O4. 2NO2N2O42.00 mol of dinitrogen tetroxide was sealed in a container at 350 K. After equilibrium had been established the total pressure was 140 kPa and the mixture of gases contained 1.84 mol of dinitrogen tetroxide. Give the expression for the equilibrium constant, Kp, for this equilibrium. Kp = Calculate the number of moles of NO2 present at equilibrium. Calculate the total number of moles of gas present at equilibrium and hence the mole fraction of each gas present at equilibrium. Calculate the partial pressure of each gas present at equilibrium. Calculate the value of the equilibrium constant, Kp, at 350 K. Give your answer to three signifi cant fi gures and include the units. Kp = units =
9701_s14_qp_23
THEORY
2014
Paper 2, Variant 3
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Questions Discovered
350