Unit 4 - Lesson 7: Burning Hydrocarbons Flashcards
What is combustion?
Combustion is the burning of a fuel, normally in oxygen.
Is a combustion reaction endothermic or exothermic and why?
It’s exothermic because it produces heat energy (exothermic reactions release heat energy).
What does the combustion of a hydrocarbon produce?
Heat energy.
What do complete combustions of hydrocarbons produce?
Carbon dioxide, water, and energy.
When does complete combustion of hydrocarbons occur?
When there’s plenty of oxygen.
Write out a chemically balanced equation for the complete combustion of butane (hydrocarbon). This is an example question.
2C4H10 + 13O2 –> 8CO2 + 10H2O + energy
Butane + Oxygen Gas –> Carbon Dioxide + Water + energy
In this example, this has been balanced.
There are 8 carbon on each side.
There are 20 hydrogen on each side.
There are 26 oxygen on each side.
How do you write a chemically balanced equation for complete combustion?
The reactants will be your fuel (the hydrocarbon) + oxygen gas.
The products will be carbon dioxide, water and heat energy.
So:
Hydrocarbon + O2 –> CO2 + H2O + energy
When does incomplete combustion occur?
When there’s less oxygen.
What is produced from incomplete combustion?
Carbon monoxide (CO) and sometimes carbon are produced.
What can we see evidence of incomplete combustion with?
Soot (carbon)
We can use Bunsen burners to demonstrate incomplete and complete combustion (air hole closed for incomplete combustion because less O2 to burn gas AND air hole open for complete combustion because more O2 to burn gas). What colour will the flame be if it’s complete combustion and what colour will the flame be if it’s incomplete combustion?
If it’s complete combustion, the flame will be blue.
If it’s incomplete combustion, the flame will be yellow.
If you place a boiling tube near a yellow flame, what will you notice?
Soot particles on the tube.
Why is carbon monoxide bad?
CO is very poisonous. It binds to red blood cells, preventing them from carrying oxygen to the body. If oxygen is prevented from reaching the brain or heart, death can occur.
What is carbon monoxide often produced by and why?
Cars because there’s little O2 inside the engine where the fuel is combusted.
Describe CO (carbon monoxide).
It’s colourless and odourless.
What do cars have to convert CO to CO2? What is the benefit and detriment of this?
Cars have catalytic converters which convert the CO to CO2. This helps humans, but not the greenhouse effect.
How does burning hydrocarbons increase global warming?
Burning hydrocarbons produces carbon dioxide, a greenhouse gas, which increases global warming.
What impurities does crude oil often contain?
Sulfur & nitrogen.
When sulfur and nitrogen combust at high temperature, for example in a power plant, what is produced?
Nitrogen oxides & sulfur dioxide. Different nitrogen oxides can be produced, such as nitrogen dioxide and nitrogen oxide, so we collectively refer to them as NOx where x can be a different number.
If SO2 or NOx react with water in the air, what is produced?
Acids are produced (sulfuric acid and nitric acid).
If sulfuric acid and nitric acid fall as rain, what is this rain called and what pH is this type of rain?
It’s called acid rain (rain with a pH lower than 5.6)
Why is clear rainwater already slightly acidic?
Clear rainwater has a pH of 5.6. It’s slightly acidic due to carbon dioxide (CO2) in the air mixing with water to make carbonic acid.
Write the chemical equations for the following combustion reactions:
(a) Sulfur Dioxide
(b) Nitrogen Monoxide
(c) Nitrogen Dioxide
(a) S (s) + O2 (g) –> SO2 (g)
(b) N2 (g) + O2 (g) –> 2NO (g)
(c) 2NO (g) + O2 (g) –> 2NO2 (g)
Finish this chemical equation:
SO2 (g) + H2O (l) –> ???
SO2 (g) + H2O (l) –> H2SO3 (aq)
What does SO2 and H2O without O2 produce?
Sulphurous acid (H2SO3)
Write the chemical equation for the production of acid rain from SO2.
2SO2 (g) + 2H2O (l) + O2 (g) –> 2H2SO4 (aq)
What are the negative impacts of acid rain on the environment and man-made things?
Acid rain damages lakes and kills fish (and sometimes all life). Trees are also hit particularly hard. Acid rain harms vegetation.
Acid rain corrodes statues and other architecture made of things like marble, limestone and iron.
Write an equation for limestone (calcium carbonate) and sulfuric acid.
CaCO3 (s) + H2SO4 (aq) –> CaSO4 (s) + H2O (l) + CO2 (g)
Metal carbonate + acid –> salt + water + carbon dioxide
How can acid rain be reduced? What method can be used?
By removing sulfur and nitrogen from the fuel. This is achieved by using a method called SCRUBBING and catalytic converters.
