Chemical reactions

Question 1

How do catalysts affect rate of reaction?

Answer 1

The mass of a catalyst at the beginning and end of a reaction is thesameand they do not form part of the equation. Different processes require different types of catalysts, but they all work on the same principle of providing adifferent pathwayfor the reaction to occur that has alower activation energy. This means a higher proportion of the reactant particles have energy greater than the activation energy and will result in more successful collisions per second. Normally onlysmallamountsof catalysts are needed to have an effect on a reaction

Question 2

Reversible reactions involving hydrated compounds

Answer 2

Reversible reactions involving hydrated compounds can be influenced by the application or removal of heat. When hydrated compounds are heated, the water molecules that are bound to the compound can be released, causing the compound to become anhydrous. This can shift the equilibrium of the reaction towards the products. On the other hand, if the hydrated compound is cooled, it can cause the water molecules to rebind with the compound, shifting the equilibrium towards the reactants.

Question 3

Reversible reactions involving anhydrous compounds

Answer 3

Reversible reactions involving anhydrous compounds such as copper(II) sulfate and cobalt(II) chloride can be influenced by the addition or removal of water. When anhydrous compounds are exposed to water, they can undergo a hydration reaction and become hydrated. This can shift the equilibrium of the reaction towards the products. However, if water is removed from the system, it can cause the hydrated compound to become anhydrous again, and shift the equilibrium towards the reactants.

Question 4

Symbol equation of haber process

Answer 4

N2(g) + 3H2(g) ⇌ 2NH3(g)

Question 5

Symbol equation for conversion of sulfur dioxide to sulfur trioxide

Answer 5

2SO2(g) + O2(g) ⇌ 2SO3(g)

Question 6

Sources of sulfur dioxide and oxygen for contact process

Answer 6

sulfur dioxide
- roasting sulfide ore
- burning sulfur in the air

oxygen
- air

Question 7

Why contact process is done with these conditions?

Answer 7

• High temperature decreases yield (favours endothermic) yet low temperatures gives low rate of reaction. 450 ºC is a compromise temperature between having a lower yield of products but being made more quickly. Additionally, the catalyst doesn’t work under 400 degrees
• The position of the equilibrium is already far to the right so high pressure is expensive, dangerous and unnecessary

Question 8

Why haber process is done with these conditions?

Answer 8

• Higher pressure increases yield but 400atm needs expensive more powerful pumps so 200atm is safer and saves money
• Exothermic reactions favour lower temperatures but the reaction is too slow while the higher temperature proceeds at faster rate but yield is low. So, 450 ºC is a compromise temperature between having alower yieldof products but being made more quickly
• The presence of a catalyst doesnotaffect the position of equilibrium but it does increase therateat which equilibrium is reached. As a result, theconcentrationof reactants and products is nevertheless thesameat equilibrium as it would be without the catalyst. So a catalyst is used as it helps the reaction reach equilibrium quicker.

Answer 9

Potassium iodide, KI, is areducingagent which is often used to test for the presence ofoxidisingagents. When added to an acidified solution of an oxidising agent such as aqueous chlorine or hydrogen peroxide (H2O2), the solution turns ared-browncolour due to the formation of iodine, I2

Question 10

Net neutralisation equation

Answer 10

H+ (aq) + OH-(aq) → H2O(l)

Question 11

What does pH measure?

Answer 11

pH is a measure of the concentration of H+ions in solution

Question 12

Methods of preparing soluble salts

Answer 12

acid reaction with an alkali by titration (use this when doing ammonium, sodium, potassium because they are extremely soluble)
acid reaction with excess metal
acid reaction with excess insoluble base
acid reaction with excess insoluble carbonate

Question 13

How to prepare an insoluble salt?

Answer 13

Dissolve soluble salts in water and mix together using a stirring rod in a beaker. Filter to remove precipitate from mixture. Wash the residue with distilled water to remove traces of other solutions. Leave in an oven to dry

Question 14

What happens to metallic character as you move across the periodic table?

Answer 14

The metallic character of the elementsdecreasesas you move across a Period on the Periodic Table, fromlefttoright, and itincreasesas you move down a Group