Chemistry

Semester. 2 Chemistry topic test -> Organic Chemistry

What is Energy?

The capacity to do work or cause change

What is Energy Consumption?

Energy consumption refers to all the energy used to perform an action, manufacture something, or simply inhabit a building

Direct vs Indirect energy use

• Direct energy use refers to the energy that is immediately consumed in the moment

  • Eg: Turning on a light

• Indirect energy use refers to the energy that is consumed in the creation or transport of goods and services - the user does not directly use the energy, but causes the energy use elsewhere

  • Eg: Energy used to manufacture a lightbulb

What are Fossil Fuels?

• Non-renewable resources made from the remains of plants and animals that died millions of years ago and have been subjected to immense heat and pressure causing them to turn into a carbon-rich fuel

• Three types: coal, oil, natural gas

What happens to the concentration of CO₂ in the atmosphere when we burn fossil fuels?

Burning fossil fuels releases large amounts of CO₂ into the atmosphere at a faster rate than it can be removed - this causes the overall CO₂ concentration to increase

Describe the Greenhouse Effect

1. Earth’s surface absorbs visible light from the sun & increases in temperature

2. Earth’s surface emits infrared radiation, most of which passes through the atmosphere

3. Some infrared radiation is absorbed by molecules of greenhouse gas

4. These molecules of greenhouse gas increase in vibrational energy

5. Increased vibrations causes more collisions with other molecules of gas

6. Kinetic energy of gases in the atmosphere increases causing the temperature of the atmosphere to increase

Effects of the Greenhouse Effect

Global:

• Greenhouse effect maintains a relatively warm average global temperature, whereas enhanced greenhouse effect causes average surface temperature to increase, causing extreme weather

• Greenhouse effect keeps water moving through the water cycle, but enhanced greenhouse effect causes sea levels to rise & flood coastal regions due to melting ice sheets

Local:

• Greenhouse effect creates stable biomes with predictable weather, but enhanced greenhouse effect causes water scarcity and wildfire risks as the temperature continues to increase

Common Greenhouse Gases

• Carbon Dioxide - CO₂

• Methane - CH₄

• Nitrous Oxide - N₂O

• Chlorofluorocarbons (CFCs)

• Hydrofluorocarbons (HFCs)

What is Organic Chemistry?

The study of compounds based on carbon atoms and their structures, properties, and reactions

Process of Fractional Distillation

1. Crude oil is heated until most of it evaporates and turns into a gas, where it is pumped into the fractionating column

2. Column is hot at bottom, cool at top, vaporized oil rises

3. When a substance reaches a height in the column where the temperature is equal to its boiling point, it condenses to form a liquid

4. Crude oil is then separated into different fractions at different heights, each fraction contains hydrocarbons with similar boiling points

5. Heavy fractions with longer molecular chains condense near the bottom, lighter fractions with shorter molecular chains condense near the top

Boiling Point

The temperature at which a substance changes from a liquid into a gas (or gas to liquid)

Viscosity

How difficult it is for a liquid to flow

Volatility

How easy it is for a substance to change into a gas

Flammability

How easy it is for a molecule to catch fire and burn in the air

Longer chain hydrocarbons

• High boiling point

• High viscosity

• Low volatility

• Low flammability

Shorter chain hydrocarbons

• Low boiling point

• Low viscosity

• High volatility

• High flammability

Fractions within a fractionating column (must be in order)

1. Refinery gas

2. Petrol

3. Naptha

4. Kerosene

5. Diesel

6. Fuel oil

7. Lubricating oil

8. Residue/Bitumen

Alkanes

• Homologous series of hydrocarbons that contain only carbon-carbon single bonds

• Are saturated

• General formula: C_nH_2n+2

Alkenes

• Homologous series of hydrocarbons that contain at least one carbon-carbon double bond

• Are unsaturated

• General formula: C_nH_2n

Alkynes

• Homologous series of hydrocarbons that contain at least one carbon-carbon triple bond

• Are unsaturated

• General formula: C_nH_2n-2

Cyclos

• Cycloalkanes general formula: C_nH_2n

• Cyclocalkenes general formula: C_nH_2n-2

• Cycloalkynes general formula: C_nH_2n-4

• Cyclo- molecules are carbon atoms bonded in rings & double/triple bonds are always between first & second carbon molecule

Saturated vs Unsaturated hydrocarbons

• Saturated hydrocarbons contain only single carbon-carbon bonds, and hold the maximum possible number of hydrogen atoms

• Unsaturated hydrocarbons contain at least one double or triple bond, and have fewer hydrogen atoms because multiple bonds take up the space where hydrogen atoms could attach

Isomers

• Isomers are molecules with the same molecular formula, but in which the atoms are arranged differently

• Chain isomers are where the carbon chain is arranged differently

  • Eg: Methylpropane has the same molecular formula as butane, but they differ in carbon chain structure

• Positional isomers exist in alkenes with four or more carbon atoms where the same funcional groups differ from each other

  • Eg: But-1-ene and but-2-ene have the same molecular formula, but different functional groups due to the placement of the double bond

What is a functional group?

A specific group of atoms within a molecule that is responsible for the typical chemical reactions of that molecule (in hydrocarbons they are the types of carbon-carbon bonds or ring like structures)

Incomplete vs Complete combustion reactions

• Complete combustion reaction:

  • hydrocarbon + oxygen → carbon dioxide + water

  • C_XH_Y + O₂ → CO₂ + H₂O

• Incomplete combustion reaction:

  • hydrocarbon + oxygen → carbon monoxide + soot (carbon) + water

  • C_XH_Y + O₂ → CO + C + H₂O

Enthalpy

• The enthalpy of a system is a quantitative measure of the potential energy stored in a system

• The enthalpy change of a system is the heat energy exchange with it surroundings

Exothermic reactions

• Chemical potential energy (enthalpy) from the system is released into the surroundings as thermal energy → increase in temperature

• Products have less enthalpy than reactants → enthalpy of system decreases

• ∆H (Delta H) is negative

Endothermic reactions

• Thermal energy from the surroundings is absorbed into the system as chemical potential energy (enthalpy) → decrease in temperature

• Products have more enthalpy than reactants → enthalpy of system increases

• ∆H (Delta H) is positive

Activation Energy

The energy required for reactants to be able to react

Catalysts

• Increases rate of reaction by reducing activation energy so a greater proportion of reactant particles can react at any given temperature

• Takes part in reaction but not consumed so can be reused

• Produce the same amount of product at a faster rate & lower temperature