Fuels Flashcards

All 41 cards in this deck

What is a hydrocarbon?

A compound that contains carbon and hydrogen only.

True or false? Ethanol, $\mathrm{C_2H_5OH}$, is a hydrocarbon.

False. It contains oxygen as well as carbon and hydrogen, so it is not a hydrocarbon.

What is crude oil?

A complex mixture of hydrocarbons, whose molecules have carbon atoms arranged in chains or rings.

True or false? Crude oil is a compound of different hydrocarbons.

False. Crude oil is a mixture of hydrocarbons, not a compound.

What does it mean to say crude oil is a finite resource?

It is being used up far faster than it forms, so supplies will eventually run out.

Apart from fuels, what important use does crude oil have?

It is the feedstock (raw material) for the petrochemical industry.

Which fuels are non-renewable fossil fuels obtained from crude oil, and which fossil fuel is found in natural gas?

Petrol, kerosene and diesel oil come from crude oil; methane is found in natural gas.

Name the six main fractions from crude oil, in order from the top of the fractionating column to the bottom.

Gases, petrol, kerosene, diesel oil, fuel oil, bitumen.

What are the steps in the fractional distillation of crude oil?

e.g. separating a crude oil containing petrol and bitumen

1. Heat the crude oil so that it vaporises, and feed it into the column.
2. Vapours rise up the column, which is hot at the bottom and cooler at the top.
3. Each fraction condenses where the temperature equals its boiling point — bitumen at the hot bottom, petrol higher up where it is cooler.

True or false? The fractionating column is hottest at the top.

False. It is hottest at the bottom and coolest at the top.

What is the kerosene fraction used for?

As a fuel for aircraft (jets).

What is the diesel oil fraction used for?

As a fuel for some cars, lorries and trains.

Which crude oil fraction is used as a fuel for large ships and in some power stations?

Fuel oil.

Which crude oil fraction is used to surface roads and roofs?

Bitumen.

What are the four features of a homologous series?

Same general formula; neighbouring members differ by $\mathrm{CH_2}$; gradual variation in physical properties (e.g. boiling point); similar chemical properties.

Which homologous series are the hydrocarbons in crude oil fractions mostly members of, and what is its general formula?

Alkanes, general formula $\mathrm{C_nH_{2n+2}}$.
e.g. $n = 4$ gives $\mathrm{C_4H_{10}}$.

As the number of carbon atoms in a hydrocarbon molecule increases, what happens to its boiling point?

It increases.

As hydrocarbon molecules get longer, what happens to their viscosity?

Viscosity increases — they become thicker and flow less easily.

As hydrocarbon molecules get longer, what happens to their ease of ignition?

They become harder to ignite (less flammable) and burn with a smokier, sootier flame.

True or false? Members of the same homologous series have similar chemical properties.

True. They react in similar ways, although their physical properties vary gradually.

What are the products of the complete combustion of a hydrocarbon fuel?

Carbon dioxide and water, and energy is given out.

How do you write a balanced equation for the complete combustion of a hydrocarbon?

e.g. propane, $\mathrm{C_3H_8}$

1. One $\mathrm{CO_2}$ per carbon, one $\mathrm{H_2O}$ per 2 hydrogens: $3\mathrm{CO_2} + 4\mathrm{H_2O}$
2. Count the oxygen atoms needed: $6 + 4 = 10$, so $5\mathrm{O_2}$
3. $\mathrm{C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O}$

Why can incomplete combustion of a hydrocarbon produce carbon monoxide and carbon?

There is insufficient oxygen to oxidise all the carbon to carbon dioxide.

What problems does soot (carbon) from incomplete combustion cause in appliances such as gas boilers?

It deposits on burners and blocks flues and pipes, wasting fuel and releasing less energy, and can cause dangerous carbon monoxide build-up.

True or false? You can tell carbon monoxide is leaking from a faulty appliance by its smell.

False. Carbon monoxide is colourless and has no smell, which is why it is so dangerous.

Where does the sulfur dioxide produced when some hydrocarbon fuels burn come from?

Sulfur impurities in the fuel, which are oxidised to sulfur dioxide during combustion.

What happens when sulfur dioxide dissolves in rain water?

It forms an acidic solution (sulfuric/sulfurous acid), producing acid rain.

State three problems caused by acid rain.

It kills trees and plants, makes lakes acidic so fish die, and corrodes metals and erodes limestone buildings and statues.

How are oxides of nitrogen formed when fuels are burned in engines?

The high temperature makes nitrogen and oxygen from the air react together.

True or false? Oxides of nitrogen from car engines come from nitrogen impurities in the fuel.

False. They form from nitrogen and oxygen in the air reacting at the high temperature inside the engine.

Which two pollutant gases from burning fuels cause acid rain?

Sulfur dioxide and oxides of nitrogen.

What is the only product formed when hydrogen burns in oxygen?

Water.

State two advantages of using hydrogen rather than petrol as a fuel in cars.

It produces only water, so no carbon dioxide, carbon monoxide, soot or sulfur dioxide; and it can be made from water, which is not a finite resource.

State two disadvantages of using hydrogen rather than petrol as a fuel in cars.

Hydrogen is hard to store and transport safely (explosive gas, needs high pressure tanks) and there are very few hydrogen filling stations.

True or false? Using hydrogen as a car fuel means no carbon dioxide is released anywhere.

False. Carbon dioxide may still be released when the energy used to manufacture the hydrogen comes from fossil fuels.

What is cracking?

Breaking down larger, saturated hydrocarbon molecules (alkanes) into smaller, more useful ones, some of which are unsaturated (alkenes).

Why is cracking necessary?

The supply of the long-chain fractions (e.g. fuel oil) is greater than the demand, while demand for short-chain fractions such as petrol is greater than the supply.

What conditions are used for cracking alkanes?

A high temperature (heat) and a catalyst.

How do you find the missing molecule in a cracking equation?

e.g. $\mathrm{C_{10}H_{22} \rightarrow \text{?} + C_2H_4}$

1. Carbons must balance: $10 - 2 = 8$
2. Hydrogens must balance: $22 - 4 = 18$
3. Missing molecule is $\mathrm{C_8H_{18}}$.

True or false? All the products of cracking an alkane are alkanes.

False. Cracking produces smaller alkanes and at least one unsaturated alkene.

In cracking, what is meant by a saturated and an unsaturated hydrocarbon?

Saturated = only single carbon–carbon bonds (alkanes); unsaturated = contains at least one carbon–carbon double bond (alkenes).