[UNIT 3] CHEM - Energy
L1 - Energy (J) Resources
Define ‘renewable’ and ‘non-renewable’ energy sources using examples
Renewable | Non-renewable | |
Definition | The source can be replaced within a human lifetime | The soruce cannot be replaced or takes much longer than a human lifetime to replace |
Examples |
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Explain each type of energy source
Energy Resources | Category | Environmental Impacts, Ethics, Reliability and Other Information |
Biofuel | Renewable | Large areas of land needed for growing fuel crops. This can be at the expense of food crops in poorer countries |
Wind | Renewable | Does not provide a constant source of energy. Turbines can be noisy/dangerous to build. Some people think that turbines ruin the appearance of the country side |
Water (hydro-electricity) | Renewable | Requires large aread of land to be flooded, altering ecosystems and displacing the people that live there. Can block access to ports for shipping |
Geothermal | Renewable | Only availiable in a limited number of places where hot rocks can be found close to the surface e.g., iceland |
Tidal | Renewable | Variations in tides affect output. Have a high initial set-up cost. Can alter habitats / cause problems for shipping |
Solar | Renewable | Depends on light intensity, so no power produced at night. High cost in relation to power output |
Nuclear fuel | Non-renewable | Produces radioactive waste but no other emissions. Costly to build and decommision. Reliable output. |
Fossil fuels (coal, oil and gas) | Non-renewable | Burning produces greenhoue gases (CO2) and contributes to acid rain. Reliable output. Provides a major source of energy for transportation. Can cause serious environmental damage. Releases toxic gases and pollutants into the atmosphere. |
L2 - Exothermic and endothermic theory
Outline what happens to energy during ‘exothermic’ and ‘endothermic’ reaction
Exothermic Reactions | Endothermic reactions |
Exothermic reactions transfer energy to the surroundings and temperature of the surrounds increases. (exo - exits the system) | Endothermic reactions absorb energy from the surroundings and temperature of the surrounds decreases (no fun pun, opposite of exothermic) |
Examples include:
| Examples include:
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Collect qualitative and quantitative data to determine is the reaction is exothermic or endothermic
Exothermic Reactions | Endothermic reactions | ||
Question | Answer | Question | Answer |
What are ‘thermite reactions’? Is it an ‘exothermic’ or ‘endothermic’ reaction? | Exothermic reactions that realisease large amounts of energy are called “thermite reactions” | Which chemicals were used to carry out the reaction in the video? (example endothermic) | Barium hydroxide and ammonium chloride |
What is an example of a thermite reaction? | The reaction between aluminium powder and iron(III) oxide | What happened to the temperature of the reaction after mixing the two chemicals? | The temperature drops from 22℃ to -25℃ |
Describe the reaction. What energy changes did you observe? | Initially the ignited spark produces heat which, when reaches the reaction mixture in the metal cup produces and extremely exothermic reaction, The heat produced in the reaction melts the iron in the can | Describe the reaction. What did you observe when the beaker was placed on the wooden block? | The drop in temperature freezes the water between the flask and the wooden block, sticking the two together |
How did the temperature chnage from the beginning to the end of the reaction? Use the words ‘increase’ or ‘decrease’ | The temperature has increase significantly from the beginning to the end of the reaction | Is the an ‘endothermic’ or ‘exothermic’ reaction? | Endothermic reaction |
Challenge Question | Challenge Answer | Challenge Question | Challenge Answer |
What are the advantages of this reaction for railway construction? | The molten iron can be used to fix broken rails | What caused the temperature drop in this reaction? | More heat energy has taken in when breaking the bonds was was released when making the new bonds of the products, the reaction is endothermic |
Suggest real life examples of exothermic reaction
Exothermic Reactions | Endothermic reactions |
Self heating cans | Melting of ice |
Hand warmers | Baking |
Fireworks | Evaporating water |
L3 - Energy graphs of endothermic and exothermic reactions
Explain using energy diagrams why some reactions are exothermic and others are endothermic
In an exothermic reaction, the products are at a lower energy than the reactants.
The difference between the energy of the reactants and the energy og the products is called the enthalpy change (△H) of the reaction
For an exothermic reaction, the enthalpy change is always negative
Why are some reactions endothermic and others are exothermic?
Chemical reactions involve bond breaking and bond making. The balance between those two processes, bond breaking and bond making, determines whether a reaction is endothermic or exothermic
Exothermic Reactions | Endothermic reactions |
Negative enthalpy change (the system loses [heat] energy) | Positive enthalpy change (the system gains [heat] energy) |
If there is an overall decrease in the amount of energy in the system, an exothermic reaction takes place | If there is an overall increase in the amount if energy in the system, an endothermic reaction takes place |
An increase in temperature of the reaction mixture (outside the system) is evidence of exothermic reaction | A decrease in temperature of the reaction mixture (outside the system) is evidence of exothermic reaction |
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Activation energy
The activation energy is the minimum amount of energy required for a reaction to take place
This can be represented on the energy profile as a ‘hump’. This shows how much energy is needed for the reactants to react and become products
Analyze quantitative data to determine is a reaction is exothermic or endothermic
L4 - Bond enthalpy
Define ‘bond enthalpy’
Bond breaking | Bond formation |
Endothermic and postive △H (temp of the reaction mixture decreases) | Exothermic and negative △H (temp of the reaction mixture increases) |
Each type of bond requires a different amount of energy to break and releases a different amount of energy when reformed. This is known as bond enthalpy (kJ/mol)
Estimate the enthalpy change of a reaction using bond enthalpies
Formula: △H = (bonds breaking) - (bonds making)
Examples of how to calculate the enthalpy change of a reaction (△H) | |
L5 - Specific heat capacity
Define ‘Specific heat capacity’
Definition
The amount of energy (J) that is needed to raise the temperature of 1kg of a substance by 1℃ or 1K
Formula
q=mcT
q= The amount of energy supplied (Joules)
m= The mass of the substance (Kg)
c= The specific heat capacity of the material
T= The change in temperature (℃ or 1K)
Apply understanding of SHC in calculations
words
Words
Words
L6 - Complete and incomplete combustion of alcohols
Outline the difference between complete combustion and incomplete combustion
What is combustion
Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. The original substance is called the fuel, and the source of oxygen is called the oxidizer.
Describe the necessary conditions for a combustion reaction to take place
Three things are required in proper combination before ignition and combustion can take place - heat, oxygen and fuel. There must be heat (ignition temperature) to start and continue the combustion process
Outline, using the fire triangle, how fire can be distinguinshed
Each side of the triangle represents one of three components needed to have a fire – oxygen, fuel and heat. Fire is a chemical reaction and without one of these components, fire cannot exist or be sustained.
What are the products of a combustion reaction
Regardless of the type of hydrocarbon, combustion with oxygen produces 3 products: carbon dioxide, water and heat,
Complete combustion | Incomplete combustion |
Happens when there is a good supply of oxygen. Carbon and hydrogen atoms in the fuel react with oxygen in an exothermic reaction: carbon dioxide and water are produced. Energy (heat) is given out | When there is insufficient supply of air. Durong incomplte combustion part of the carbon is not completely oxidized producing soot or carbon monoxide (CO) |
Fuel+O2CO2+H2O | Fuel+O2CO+H2O |
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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. This reduces the capacity of the blood to carry oxygen. |
L7 - Why do substances change state
Recall the three states of matter
When drawing the arrangement of particles in the 3 states of matter, you MUST include at least 6 particles in each diagram
Outline the difference between heat and temperature
Heat is a form of energy (J). Heat always transfers from a higher temperature object to a lower temperature object
Temperature (K or ℃) is a measure of the avergae kinetic energy of particles in a substance
Absolute temperature (K) is directly proportional to the average kinetic energy of the particles in a substance
Interpret cooling curved in terms of energy
