3. Reactions & processes

Question 1

“Energy is neither created nor destroyed, but is converted from one form to another.” What is this?

Answer 1

The law of conservation of energy.

Question 2

What are some different forms of kinetic and potential energy?

Answer 2

Question 3

How does a light in our homes convert energy?

Answer 3

It changes electricity into light and heat.

Question 4

What is an efficient conversion of energy?

Answer 4

One that releases only a small amount of heat and a large amount of the desired energy.

Question 5

What is the formula for the efficient conversion of energy?

Answer 5

Question 6

What is heat?

Answer 6

The measure of kinetic energy in an object. Increasing the temperature increases the kinetic energy.

Question 7

What is chemical potential energy?

Answer 7

Chemical potential energy is stored in the bonds between the atoms and molecules of a substance.

If we were able to break these bonds, the energy stored in them could be converted into other forms of energy. For example, burning wood releases the chemical potential energy stored in the bonds between the wood particles and converts it into heat and light energy.

Question 8

When two atoms are chemically bonded they have low what?

Answer 8

Kinetic energy.

Question 9

In order to break the chemical bond, we need to increase the kinetic energy of the two atoms so that it can overcome the inter-atomic forces. We require some what energy input?

Answer 9

Something like heat in order to increase the kinetic energy of the atoms and break the chemical bond.

Question 10

The amount of energy input required to break the bond is referred to as what?

Answer 10

The activation energy.

Question 11

Breaking a chemical bond always requires heat from the environment and as such is always classified as a what?

Answer 11

Endothermic process.

When heat is taken from the environment it is referred to as an endothermic process.

“Endo” is a prefix derived from Greek which means “within, absorbing or containing.”

So from the viewpoint of the system, it has taken in (absorbed) heat from the environment making it an endothermic process.

Question 12

In order for chemicals to bond, what must they release into the environment?

Answer 12

Kinetic energy (usually heat).

Question 13

When heat is released into the environment it is referred to as what process?

Answer 13

An exothermic process.

Question 14

What is another name for combustion?

Answer 14

Burning.

Question 15

What is the general equation for the burning of fossil fuels?

Answer 15

Hydrocarbon + Oxygen = Heat energy

Question 16

What happens in a complete combustion?

Answer 16

Blue flame, little soot or smoke. Heat and carbon dioxide are also produced.

Question 17

CO2​ emissions impact human health by displacing oxygen in the atmosphere. This increased atmospheric \tCO2​ concentrations and overall air pollutants makes breathing more difficult for people.

Along with respiratory disease, elevated atmospheric CO2​ concentrations increases the risk for cardiovascular disease, cancer and adverse birth outcomes.

In 2015, it was reported that how many deaths worldwide (or one in six deaths) were due to air-pollution?

Answer 17

9 million.

Question 18

In a combustion reaction, a fuel is combusted (burnt) in the presence of oxygen (an oxidiser) to produce the products of combustion and heat energy.

In incomplete combustion, these products are what?

Answer 18

Solid carbon particles (C), carbon monoxide (CO) and water (H2​O).

Question 19

When does incomplete combustion occur?

Answer 19

When the supply of oxygen is poor.

Question 20

What are the physical signs of an incomplete combustion?

Answer 20

This carbon is released as solid particles known as soot. These particles make up the visible part of smoke that is characteristic of incomplete combustion reactions. Incomplete combustion reactions will also produce a yellow flame caused by the glowing of the hot carbon particles.

Question 21

When is an incomplete combustion more likely?

Answer 21

The longer the hydrocarbon, the more likely it is to undergo incomplete combustion.

Smaller chain hydrocarbons have a higher chance of undergoing complete combustion.

This is because there is more likely to be enough oxygen for all the carbon atoms to gain two oxygen atoms to form CO2​.

Question 22

The longer the hydrocarbon, the more likely what?

Answer 22

That is, the bigger the hydrocarbon, the more likely you are to get a yellow, smoky flame.

Question 23

What is more likely to undergo incomplete combustion - alkanes or alkenes?

Answer 23

Alkenes are more likely to undergo incomplete combustion when compared to alkanes. This is because alkenes have a higher ratio of carbon (C) atoms to hydrogen (H) atoms compared to alkanes. Any available O2​ is used to form water, and the remaining oxygen has a high number of C atoms to react with. Some C atoms will react to form CO. Once all the available O atoms have reacted, the remaining C atoms will remain unbonded and appear as soot.

Question 24

What are the harmful effects in the environment of incomplete combustion?

Answer 24

Carbon monoxide production from incomplete combustion of fuels results in the formation of smog. The ozone in smog has been shown to inhibit plant growth and cause widespread damage to crops and forests.

Question 25

What is one good reason we prefer complete combustion?

Answer 25

Carbon monoxide is a poisonous gas, which is one reason why complete combustion is preferred to incomplete combustion.

Carbon monoxide is absorbed in the lungs and binds with the haemoglobin in our red blood cells. Oxygen is carried throughout the blood by haemoglobin.