Equilibria Flashcards

1
Q

Sulfuric acid is manufactured by the Contact Process.In this process, sulfur dioxide reacts with oxygen. The equation for the equilibrium that is established isSO2(g) + 1/2O2(g) SO3(g) ΔH = –98kJmolState and explain the effect of a decrease in temperature on the equilibrium yield of SO3and why?

A

(Yield) increases / goes up / gets moreThe (forward) reaction / to the right is exothermic or gives out / releases heatOR The reverse reaction / to the left is endothermic or takes in /absorbs heatThe (position of ) equilibrium shifts / moves left to right to oppose the decrease in temperature

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2
Q

Give two features of a reaction at equilibrium

A
  1. Concentration(s) (of reactants and products) remain or stay constant / the same2. Forward rate = reverse / backward rate
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3
Q

Write an equation for the reaction of concentrated sulfuric acid with potassium bromide to form potassium hydrogensulfate and hydrogen bromide.

A

KBr + H2SO4 ——>KHSO4 + HBr

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4
Q

Bromine is one of the products formed when concentrated sulfuric acid reacts with hydrogen bromide.Write an equation for this reaction.State the role of sulfuric acid in this reaction.

A

2HBr + H2SO4 ——>Br2 + SO2 + 2H2OOxiding agent or electron acceptor or oxidanti.e. to oxidise the bromide ion

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5
Q

Concentrated sulfuric acid is used in a two-stage process to convert 2-methylpropene into 2-methylpropan-2-ol.Stage 1 (CH3)2C CH2 + H2SO4 —–>(CH3)2C(OSO2OH)CH3 Stage 2 (CH3)2C(OSO2OH)CH£ + H2O —–>(CH3)2C(OH)CH3 + H2SO4Name this type of conversion in stage 1 and 2State the overall role of sulfuric acid in this conversion.

A
  1. Electrophilic addition2.Hydrolysis3. Catalyst
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6
Q

State the meaning of the term rate of reaction.

A

Change in concentration of a substance / reactant / product in unit time

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7
Q

Hydrogen gas is collected when a sample of magnesium reacted with an excess of dilute hydrochloric acid.The rate of this reaction can be studied by measuring the time it takes for a given volume of hydrogen to be collected. In terms of collision theory explain why, at a fixed temperature, the rate of this reaction doubles when the concentration of the hydrochloric acid doubles.

A

Twice / double as many particles / hydrogen ions (in a given volume) causes twice / double as many effective / successful collisions (in a given time)

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8
Q

State the meaning of the term activation energy.

A

The activation energy is the minimum energy for a reaction to start

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9
Q

A study of equilibrium is important for understanding chemical reactions.State Le Chatelier’s principle.

A

(When a system / reaction in equilibrium is disturbed), the (position of) equilibrium shifts / moves in a direction which tends to reduce the disturbance

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10
Q

State the meaning of the term catalyst. Explain, in general terms, how catalysts work.

A

A substance that speeds up the reaction / alters the rate but is chemically unchanged at the end / not used upCatalysts provide an alternative route / alternative pathway / different mechanismthat has a lower activation energy / Ea ORlowers the activation energy / Ea

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11
Q

State the effect, if any, of a catalyst on the time taken to reach equilibrium.

A

(Time is) less / shorter / decreases / reduces

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12
Q

State the effect, if any, of a catalyst on the position of an equilibrium.

A

None

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13
Q

Ammonia is manufactured by the Haber process in which the following equilibrium isestablished.N2(g) + 3H2(g) 2NH3(g)Give two features of a reaction at equilibrium.

A

Concentrations (of reactants and products) remain or stayconstant / the same Forward rate = Reverse / backward rate

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14
Q

Explain why a catalyst has no effect on the position of an equilibrium.

A

Catalysts increase rate of / speed up both forward andreverse / backward reactionsincrease in rate / affect on rate / speed is equal / the same

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15
Q

A sample of nitrogen dioxide gas (NO2) was prepared by the reaction of copper with concentrated nitric acid.Balance the equation for the reaction of copper with concentrated nitric acid. Cu + …….. HNO3 ———->Cu(NO3)2 + …….. NO2 + …….. H2O

A

Cu + 4HNO3 ———->Cu(NO3)2 + 2NO2 + 2H2O

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16
Q

Give the oxidation state of nitrogen in each of the following compounds. HNO3NO2

A

HNO3 (+) 5NO2 (+) 4

17
Q

Deduce the half-equation for the conversion of HNO3 into NO2 in this reaction.

A

HNO3 + H+ + e- ———>NO2 + H2O

18
Q

The following equilibrium is established between colourless dinitrogen tetraoxide gas (N2O4) and dark brown nitrogen dioxide gas.N2O4(g)  2NO2(g) ΔH = + 58 kJ mol–1 Give two features of a reaction at equilibrium

A

*Concentration(s) (of reactants and products) remain(s) constant *Forward rate = Reverse / backward rate

19
Q

Use Le Chatelier’s principle to explain why the mixture of gases becomes darker in colour when the mixture is heated at constant pressure.

A

1.The (forward) reaction / to the right is endothermic or takes in i.e. absorbs heatORThe reverse reaction / to the left is exothermic or gives out / releases heat2.The equilibrium shifts / moves left to right to oppose the increase in temperature

20
Q

Use Le Chatelier’s principle to explain why the amount of NO2 decreases when the pressure is increased at constant temperature.

A

1.There are fewer moles (of gas) on the left OR more moles (of gas) on the right.OR there is one mole (of gas) on the left and 2 moles on the right.2. The equilibrium shifts / moves right to left to oppose the increase in pressure

21
Q

An equilibrium is established between oxygen and ozone molecules as shown below. 3O2(g) 2O3(g) ΔH = +284 kJ mol–1State Le Chatelier’s principleUse Le Chatelier’s principle to explain how an increase in temperature causes an increase in the equilibrium yield of ozone (2)

A

(When a system / reaction in equilibrium is disturbed), the equilibrium shifts/moves in a direction which tends to reduce the disturbancethe (forward) reaction / to the right is endothermic or takes in heatorthe reverse reaction / to the left is exothermic or gives out heatANDThe equilibrium moves / shifts to oppose the increase in temperature

22
Q

State and explain the effect of an increase in total pressure on the rate of attainment of this equilibrium (3)

A

Increase / speed up / faster (rate of attainment of equilibrium)More particles / molecules in a given volume / space OR the particles / molecules are closer togetherOR an increase in concentration.*More / higher chance of successful / effective / productive collisions (between particles)OR more collisions / higher chance of collisions (of particles) with E>EAct

23
Q

Hydrogen reacts with nitrogen in the Haber Process. The equation for the equilibrium that is established is shown below.N2(g) + 3H2(g)  2NH3(g)Use Le Chatelier’s principle to explain why an increase in the total pressure of this equilibrium results in an increase in the equilibrium yield of ammonia.

A

(If any factor is changed which affects an equilibrium), the position of equilibrium will shift / move / change/ respond / act so as to oppose the change.