2.6 Reversible Reactions, Industrial Processes & Important Chemicals (WJEC GCSE Chemistry): Flashcards

In the Haber Process, hydrogen is obtained from methane (natural gas) and nitrogen is obtained from air.

The catalyst used in the Haber Process is iron.

True.

After ammonia is liquefied and removed, the unreacted hydrogen and nitrogen gases are recycled back into the system to increase efficiency.

In the Haber Process, ammonia is separated from unreacted gases by liquefying it. The liquid ammonia is then stored in pressurised vessels.

True.

This equation shows nitrogen and hydrogen reacting reversibly to form ammonia. The ⇌ symbol confirms the reaction is reversible.

Ammonia is separated from unreacted gases by passing the mixture into a cooling tank, where the ammonia liquefies and is removed.

The Haber Process uses 450 °C. This is a compromise because a lower temperature gives a higher yield but a very slow rate, while a higher temperature gives a faster rate but a lower yield.

True.

A higher pressure favours the forward reaction because it reduces the number of gas molecules (from 4 to 2), increasing the yield of ammonia. However, very high pressures are expensive and dangerous.

Compromise conditions are the operating conditions chosen for an industrial process that balance yield, rate of reaction, and cost, rather than optimising any single factor alone.

The Haber Process uses a pressure of 200 atm, chosen as a compromise between a high yield of ammonia and the costs and safety risks of operating at very high pressure.

In the Haber Process, the forward reaction N₂ + 3H₂ → 2NH₃ is exothermic. Using a lower temperature gives a higher yield but a slower rate.

False.

The iron catalyst increases the rate of reaction but does not change the equilibrium yield. It allows ammonia to be produced more quickly at the compromise temperature.

A very high pressure is not used because the equipment needed is very expensive and high pressures can be dangerous. The 200 atm used is a compromise between yield, safety, and cost.

The Haber Process uses a temperature of 450 °C and a pressure of 200 atm as compromise conditions.

Ammonia gas is tested for by holding damp red litmus paper near the mouth of the test tube. Ammonia turns the damp red litmus paper blue.

A pungent smell is a sharp, strong, and unpleasant odour. Ammonia has a characteristic pungent smell, but this alone is not a reliable chemical test.

False.

The pungent smell is not a valid chemical test. The correct test is to hold damp red litmus paper near the gas. Ammonia turns damp red litmus paper blue.

Ammonia turns damp red litmus paper blue.

The litmus paper must be damp because ammonia dissolves in water to form an alkaline solution. It is this alkaline solution that causes the colour change in the litmus paper.

True.

Ammonia dissolves in water to form an alkaline solution, which is why it turns damp red litmus paper blue.

When testing for ammonia from ammonium ions and sodium hydroxide, the litmus paper should not touch the sides because traces of sodium hydroxide solution could also turn the red litmus paper blue, giving a false positive result.

The Contact Process is the industrial method used to manufacture sulfuric acid from sulfur, oxygen, and water.

The catalyst used in Stage 2 of the Contact Process is vanadium(V) oxide, V₂O₅.

In Stage 2 of the Contact Process, sulfur dioxide reacts with oxygen using a vanadium(V) oxide catalyst at 450 °C to form sulfur trioxide.

False.

Sulfur trioxide is absorbed into 98% sulfuric acid to form oleum (disulfuric acid), which is then added to water. Direct addition to water would produce a dangerous fine mist of sulfuric acid.

Uses of sulfuric acid include the production of:\n\n1. Fertiliser\n2. Paint\n3. Detergent\n4. Dye\n5. Fibres\n6. Plastic

In Stage 1 of the Contact Process, sulfur is burned in oxygen to produce sulfur dioxide. The word equation is: sulfur + oxygen → sulfur dioxide.

Oleum (disulfuric acid, H₂S₂O₇) is formed when sulfur trioxide is absorbed into 98% sulfuric acid.

False.

The Contact Process uses only approximately atmospheric pressure. The equilibrium already lies far to the right (about 96% SO₃), so the extra cost of high pressure is not justified.

Oleum (disulfuric acid, H₂S₂O₇) is added to water to produce concentrated sulfuric acid.

A dehydrating agent is a substance that removes the elements of water from another substance, either by removing hydrogen and oxygen atoms or by removing water of crystallisation.

When concentrated sulfuric acid is added to sucrose, the sugar turns brown then black as carbon is formed. Water vapour is released, and the carbon grows out of the container as a column.

True.

The reaction is highly exothermic. The heat released evaporates some of the water produced, which can be seen as water vapour escaping from the mixture.

When concentrated sulfuric acid acts as a dehydrating agent on sucrose, the hydrogen and oxygen atoms are removed, leaving behind carbon.

When concentrated sulfuric acid is added to blue hydrated copper(II) sulfate, a colour change from blue to white is observed as the water of crystallisation is removed, forming anhydrous copper(II) sulfate.

True.

Concentrated sulfuric acid acts as a dehydrating agent, removing the water of crystallisation from blue hydrated copper(II) sulfate to produce white anhydrous copper(II) sulfate.

The carbon grows out of the container because water vapour produced during the exothermic reaction becomes trapped inside the carbon, causing it to expand and rise.

Concentrated sulfuric acid can remove water of crystallisation from hydrated copper(II) sulfate. The blue crystals form white anhydrous copper(II) sulfate.

A nitrogenous fertiliser is a fertiliser that contains a source of nitrogen, which plants need to produce proteins, chlorophyll, and healthy leaves.

Plants need nitrogen to make chlorophyll and proteins and to promote healthy leaf growth.

Ammonium nitrate is produced by the reaction of ammonia with nitric acid. The balanced equation is: NH₃ (g) + HNO₃ (aq) → NH₄NO₃ (s).

Phosphorus promotes healthy root growth in plants.

True.

Ammonium ions and nitrate ions are soluble sources of nitrogen that plants can absorb, making ammonium salts and nitrates effective fertilisers.

Fertilisers are produced by neutralisation reactions. For example, ammonia reacts with sulfuric acid to form ammonium sulfate, which has the formula (NH₄)₂SO₄.

False.

Potassium promotes growth and healthy fruit and flowers. It is phosphorus that promotes healthy roots.

Two soluble sources of nitrogen in fertilisers are:\n\n1. Ammonium ions, NH₄⁺\n2. Nitrate ions, NO₃^-

Ammonium ions are tested for by gently warming the solution with sodium hydroxide solution. Ammonia gas is released, which turns damp red litmus paper blue.

True.

Sodium hydroxide solution is a source of hydroxide ions, OH^-. These react with ammonium ions when warmed, releasing ammonia gas.

To test for ammonium ions, gently warm the solution with sodium hydroxide solution. The gas released turns damp red litmus paper blue.

The ammonium ion is a positively charged ion with formula NH₄⁺, formed when ammonia dissolves in or reacts with water or acids.

Ammonia gas, NH₃, is released when ammonium ions are warmed with sodium hydroxide solution.

False.

The solution is only gently warmed, not boiled. Gentle warming is sufficient to release ammonia gas from the reaction between ammonium ions and sodium hydroxide.

Ammonium ions, NH₄⁺, are identified by warming with sodium hydroxide solution, which provides hydroxide ions that release ammonia gas.

Eutrophication is a process in which excess nutrients from fertilisers wash into waterways, causing rapid algal growth that ultimately depletes oxygen levels and kills aquatic life.

Plants need nitrogen from fertilisers for the production of proteins and chlorophyll, and to promote healthy leaf growth.

False.

Algal blooms form a continuous layer on the water surface that blocks sunlight. This prevents underwater plants from photosynthesising, causing oxygen levels to drop.

During eutrophication, aerobic bacteria break down dead organisms and use up oxygen in the water, which can cause fish to die in large numbers.

An algal bloom is a continuous layer of microscopic plants on the surface of a waterway. It is caused by excess minerals from fertilisers washing into the water and stimulating rapid plant growth.

True.

Rainfall can leach water-soluble minerals from the soil into rivers and lakes. Fertilisers can also wash directly into waterways, both contributing to eutrophication.

Fertilisers contain nitrogen, phosphorus, and potassium, which plants need for healthy growth.

Eutrophication causes fish to die because algal blooms block sunlight, preventing photosynthesis. Oxygen levels fall as aerobic bacteria break down dead organisms. Fish require high oxygen levels to survive and die when these are depleted.