Reactivity 1.3—Energy from fuels

Question 1

What types of compounds can serve as fuels in combustion reactions?

Answer 1

Hydrocarbons (compounds containing only carbon and hydrogen) and alcohols (organic compounds with a hydroxyl group bonded to a carbon atom).

Question 2

What is required as a reactant in every combustion reaction?

Answer 2

Oxygen is required as a reactant that reacts with the fuel.

Question 3

What are the typical products of complete combustion of hydrocarbons and alcohols?

Answer 3

Carbon dioxide and water are the typical products.

Question 4

What is crucial when balancing chemical equations for combustion reactions?

Answer 4

Ensuring that the number of atoms for each element is the same on both sides of the equation, possibly adjusting coefficients for the fuel, oxygen, carbon dioxide, and water.

Question 5

Incomplete combustion

Answer 5

A fuel burns a restricted supply of oxygen and carbon monoxide and/or soot are produced.

Question 6

How do you deduce equations for the incomplete combustion of hydrocarbons and alcohols?

Answer 6

Consider the oxygen availability. Incomplete combustion occurs when there is limited oxygen, producing carbon monoxide (CO), carbon (C), and water (H₂O), instead of carbon dioxide (CO₂) and water.

Question 7

What are the possible products of incomplete combustion of hydrocarbons and alcohols?

Answer 7

Carbon monoxide (CO) and water (H₂O) or carbon (C) and water (H₂O), depending on the availability of oxygen.

Question 8

What are the differences between complete and incomplete combustion?

Answer 8

Complete combustion produces carbon dioxide (CO₂) and water (H₂O), high-temperature blue flame, no smoke. Incomplete combustion produces CO or C and H₂O, lower-temperature orange/yellow flame, and smoke.

Question 9

How do coal, crude oil, and natural gas differ in the amount of CO2 they add to the atmosphere upon combustion?

Answer 9

The CO2 released varies by fuel type due to their different compositions. Coal, crude oil, and natural gas each produce distinct amounts of CO2 per unit of energy, with equations and data available to calculate these emissions.

Question 10

How do coal, crude oil, and natural gas compare in terms of energy released per unit mass and tendencies for incomplete combustion?

Answer 10

Natural gas releases the most energy per unit mass, followed by crude oil, with coal being the least. Coal has the greatest tendency for incomplete combustion, leading to carbon monoxide and other by-products, mainly due to impurities that consume oxygen.

Question 11

What is the relationship between CO2 levels and the greenhouse effect?

Answer 11

CO2 and other gases trap infrared radiation, leading to higher global temperatures. The rise in CO2 levels, mainly from fossil fuel combustion, has resulted in a rapid increase in global temperatures, showcasing a direct link between CO2 emissions and the greenhouse effect.

Question 12

Photosynthesis

Answer 12

A process used by green plants to produce glucose (and oxygen) from carbon dioxide and water in the presence of light.

Question 13

Biofuels

Answer 13

A fuel derived directly from living matter.

Question 14

Fuel cells

Answer 14

A device that uses an external source of fuel and oxygen (or air) to transfer energy from a chemical store by electricity.

Question 15

What are the reactants and products of photosynthesis?

Answer 15

Reactants are sunlight, carbon dioxide gas, and water vapor. Products are glucose and oxygen gas.

Question 16

What is the difference between renewable and non-renewable energy sources?

Answer 16

Renewable energy sources, like solar energy and wind power, can be naturally replenished. Non-renewable energy sources, such as fossil fuels, cannot be quickly replenished.

Question 17

What are the advantages of biofuels?

Answer 17

Biofuels can offset carbon emissions through CO2 absorption during photosynthesis and result in cleaner combustion compared to fossil fuels.

Question 18

What are the disadvantages of biofuels?

Answer 18

They require large amounts of agricultural land that could be used for food production, and their combustion still releases CO2 into the atmosphere.

Question 19

Electrolysis

Answer 19

A process in which compounds are split apart by the passage of electricity through either a molten state or aqueous solution.

Question 20

How do fuel cells convert energy?

Answer 20

Fuel cells convert chemical energy directly into electrical energy through electrochemical reactions, bypassing combustion.

Question 21

What is the primary fuel in methanol fuel cells and the by-products?

Answer 21

Methanol fuel cells utilize methanol, producing carbon dioxide, water, and electricity.

Question 22

What is the primary fuel in hydrogen fuel cells and the by-products?

Answer 22

Hydrogen fuel cells operate on hydrogen gas, producing only water and electricity.

Question 23

What is the key distinction between methanol and hydrogen fuel cells?

Answer 23

The key distinction lies in the fuel source and by-products; methanol produces CO2, while hydrogen produces only water.

Question 24

How are half-equations deduced in fuel cells?

Answer 24

Identify oxidation and reduction processes, balance electrons lost in oxidation with those gained in reduction.

Question 25

What undergoes oxidation in methanol and hydrogen fuel cells?

Answer 25

Methanol is oxidized in methanol fuel cells; hydrogen gas is oxidized in hydrogen fuel cells.

Question 26

What undergoes reduction in methanol and hydrogen fuel cells?

Answer 26

Oxygen is reduced in both methanol and hydrogen fuel cells, gaining electrons.