Unit 3 AOS 1 - Energy Flashcards
types of energy?
Energy can be considered active (kinetic) or stored (potential).
what is active energy?
Active forms of energy are those currently in use to make something happen (do work).
what is stored energy?
Stored (potential) forms of energy can be used to make something happen (do work) in the future.
SI unit for energy?
The SI unit for Energy is Joules (J) but for large amounts is measured in kJ or MJ.
types of active (kinetic) energy?
- Mechanical Energy (Energy due to motion of an object)
- Electrical Energy (Energy from flow of electric charge)
- Thermal Energy (or heat energy, Is vibration or movement of particles)
- Radiant Energy (or light energy is electromagnetic energy that travels in transverse waves)
- Sound Energy (vibration transferred through an object in a wave to produce sound)
types of stored (potential) energy?
- Chemical Energy (Energy stored in bonds of atoms and molecules)
- Nuclear Energy (Energy stored in atoms’ nucleus)
- Gravitational Energy (Energy stored in an object’s height)
- Elastic Energy (Energy stored in elastic objects)
define Law of Conservation of Energy
Energy cannot be created or destroyed, however, it can be converted from one form to another.
why do we convert energy forms?
Often we convert energy forms so that the energy is in a more accessible form, or more useful form for the context needed.
are energy conversions always efficient?
Energy conversions are never 100% efficient. This means that some energy is always ‘lost’ in the conversion.
is energy ‘lost’ ever?
The energy is not actually ‘lost’ it has simply turned into an unusable/unhelpful form, typically heat.
energy efficiency formula
% efficiency = (energy obtained in desired form/energy available before conversion) × 100
define fuel
A fuel is a substance with stored energy, typically that has a high energy density/content.
how is energy in a fuel typically converted?
Chemical energy (stored) in the fuel is often converted to a high amount of thermal energy via a combustion reaction.
what are the units for energy content?
Energy density/content varies between different fuels and often recorded as kJg-1 (mixtures), kJmL-1 (mixtures) or kJmol-1 (pure substances).
characteristics of fuels?
Fuels are flammable and include substances such as: alcohols, long and short chain hydrocarbons, coal etc.
what are the main uses of fuels?
- The energy in fuels is typically used in transport.
- Foods are also a source of energy for our bodies.
what are fuels classified as when directly or indirectly sourced?
renewable or non-renewable
define renewable energy
energy sources that can be produced faster than they are used
define non-renewable energy
energy sources that are being used up faster than they can be produced
examples of renewable fuels?
- biomass
- solar
- water
- geothermal
- wind
examples of non-renewable fuels?
- molecular
- coal
- oil
- natural gas
When selecting a fuel you must consider…?
- The energy density/content of the fuel
- The environmental impacts of its sourcing and its combustion products (eg carbon dioxide is a greenhouse gas)
- Does its properties suit its use?
- Viscosity (flow)
- Melting and boiling points
what are fuels physical properties determined by?
A fuels physical properties are governed by the type and strength of its intermolecular bonding.
how is energy converted in chemical reactions?
In many chemical reactions chemical energy is converted to heat/thermal energy and vice versa.
what are the two types of chemical reactions relating to energy?
Exothermic and Endothermic
what happens in an exothermic reaction?
Exothermic reactions result in temperature increases during a reaction.
what happens in an endothermic reaction?
Endothermic reactions result in a temperature decrease during a reaction.
what do bond breaking and formation in reactions result in?
All the bond breaking and bond formation results in a unique enthalpy change (ΔH) for that reaction.
enthalpy change for exothermic?
ΔH = negative (energy released)
enthalpy change for endothermic?
ΔH = positive (energy required)
what do all chemical reactions involve?
Chemical reactions involve the rearrangement of particles (atoms/ions).
what is needed to initiate chemical reactions?
To initiate the reaction, intramolecular bonds (covalent, metallic, ionic) must be broken in the reactants. This is the activation energy, Ea, for the reaction. This requires energy (typically heat/thermal).
what is needed to form new products?
To form the products, new intramolecular bonds (covalent, metallic, ionic) must be formed. This releases energy (typically heat/thermal).
what changes when the type of bonds change?
When the types of bonds/atoms change, the energy required to break them, or released when they reform also changes.
how are endo/exo thermic reactions determined?
Comparing the energy to break bonds to the energy to form bonds determines endo/exo.
what is a thermochemical equation used for?
A thermochemical equation is used to provide important information about how energy is changing as a reaction proceeds.
Thermochemical equations must contain…?
- Balanced equation
- States for all species at room temperature
- Enthalpy change (ΔH) for the reaction, including +/- sign and units (kJ), for how energy changes between reactants and products
difference between Enthalpy change vs Energy content?
The difference between Enthalpy change for the reaction (Δ= +/- kJ) and Energy density/content/molar enthalpy of a fuel (kJmol-1) .
If coefficient in front of fuel in balanced equation = 1, what does that mean for enthalpy change and energy content?
Enthalpy change for reaction (ΔH= +/- kJ) = Energy content of fuel (kJmol-1)
If coefficient in front of fuel in balanced equation does NOT = 1, what does that mean for enthalpy change and energy content?
Enthalpy change for reaction (ΔH= +/- kJ) does NOT = Energy content of fuel (kJmol-1)
what do thermochemical equations allow for you do to in equations?
Thermochemical equations will always allow you to establish a known relationship between coefficient moles (mol) of a species (either reactant or product) and the energy (kJ) released/required when that moles of substance is burnt/produced.
what do you do in calculations once you have determined a relationship from a thermochemical equation?
This known relationship can therefore be used as a ratio to compare a new situation to. Using the cross multiply technique, in the new situation you will either be:
- Given moles (mol) and asked to find energy (kJ)
- Given energy (kJ) and asked to find moles (mol)
what happens if you are given mass in a calculation that is asking for kJmol-1?
Sometimes mass (g) can also be used, but you can always convert to/from moles by using n=m/M or even volume (mL).
what must happen in all stoichiometry calculations?
You must move between one substance and another using the mole ratio from the thermochemical equation.
what do you do if information about both reactants is known?
If mass(g) or mole(mol) info is known about both reactants, always run stoichiometry calculations (prediction about the amount of product) using the limiting reactant.
what is Hess’s Law used for?
Hess’s Law is used to find the enthalpy change (ΔH) for a given reaction by using the known enthalpy changes for related reactions.
what does Hess’s Law involve?
Involves reversing, doubling, halving etc related equations and their enthalpies and then adding them to give the desired equation and enthalpy change (ΔH).
what is the main gas produced during combustion?
The main gas produced during combustion, CO2, is a greenhouse gas.
what are greenhouse gases?
Greenhouse gases help trap the sun’s energy within the Earth’s atmosphere to maintain an appropriate temperature to support life.
what does excessive release of greenhouse gases cause?
Excessive release of greenhouse gases results in the enhanced greenhouse effect, causing global warming.
Examples of greenhouse gases?
CH4, N2O, O3, H2O(g), CO2
what is used to explain the observable properties of gases?
Gases are known to behave in predictable ways. The kinetic molecular theory is used to explain the observable properties of gases.
Typically a gas will be discussed in terms of its…?
- Volume (SI = L, or mL)
- Pressure (SI = Pa, or kPa, or atm, mmHg or bar)
- Temperature (SI = K or oC)
- Moles (mol)
what happens to gases in SLC?
Under standard lab conditions (SLC), 1 mole of any gas will occupy a volume of 24.8L (Vm)
formula for gases at SLC?
n=V/Vm
what is SLC?
- 25oC (298 K)
- 100 kPa
what is the gas constant R?
8.31 J mol-1 K-1
what happens to pressure and volume when temperature is constant in gases?
At constant T, as pressure increases, volume decreases. P1V1 = P2V2
what happens to temperature and volume when pressure is constant in gases?
At constant P, as volume increases, temperature increases. V1/T1 = V2/T2
what happens to temperature and pressure when volume is constant in gases?
At constant V, as pressure increases, temperature increases. P1/T1 = P2/T2
what is a law for temperature, pressure and volume in gases?
P1V1/T1 = P2V2/T2
what is the ideal gas law?
PV = nRT
- pressure in kPa
- temp in K
- volume in L
what is the ultimate considerations with gas fuels and energy?
Ultimately it is important to consider how much greenhouse gas is emitted when a certain amount of energy is produced from the combustion of a chosen fuel and whether the environmental trade off is sustainable and makes sense for the given application.
what is calorimetry?
Calorimetry is a practical technique used to determine either the energy content/density (kJmol-1 or kJg-1) of a chosen fuel and/or the enthalpy change (kJ) of that fuels combustion reaction.
what does calorimetry require you to know?
- Mass of water heated (g or mL)
- Specific heat capacity of water
- Temperature change of water
- Amount of fuel burnt (g or mol)
what is used in calorimetry equations?
The formula q=mcΔT and cross multiplying is used.
what can calorimetry be used for in real life applications and what units would it come out in and why?
Calorimetry can similarly be used to determine the heat of combustion for a range of foods.
Although the technique is called calorimetry, we use it determine the foods energy content in kJg-1, not in calories. Since foods are mixture kJmol-1 cannot be measured
what macromolecule has the most accessible energy and what is is used for?
The energy stored in carbohydrates is the most rapidly accessible and is used for cellular respiration.
what has calorimetry been used to determine related to foods that is in the data booklet?
Calorimetry has been used to determine the heat of combustion of macromolecules.
what are the types of carbohydrates and their energy accessibility?
Simple carbs (biscuits, lollies etc) ⇒ glucose often already available.
Complex carbs (bread, pasta etc) ⇒ starch digested/metabolised into glucose first.
cellular respiration equation
C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l) + energy
what are the two types of calorimetry?
Solution calorimetry
Bomb calorimetry
when is solution calorimetry used?
Used when a reaction is occurring in solution (eg acid/base, acid + metal)
when is bomb calorimetry used?
Used when fuels/foods are combusted or reaction occurs in gas state
what do both calorimetry techniques involve?
Both techniques involve measuring the ΔT for a known vol or mass of water, and comparing that to the known mass or moles of reactant/food.
what can units be for calorimetry and when?
kJmol-1 → for reactants with a known formula
kJg1 → for mixtures/foods where formula is not accurately known
what do both calorimetry techniques need?
Both types of calorimetry require the calorimeter to be calibrated.
what does calorimetry calibration determine?
Calibration determines how effectively the calorimeter vessel retains heat. Each calorimeter is unique and we want to know how good/effective ours is.
how can heat be lost in calorimetry?
Heat energy can be lost to the environment or into the components of the calorimeter itself.
how does calibration of calorimetry occur?
Calibration involves determining the calorimeter’s calibration factor (CF). This is done by ‘supplying’ the calorimeter with a known amount of energy and seeing what temperature change this results in.
calorimetry calibration equation and units
CF = q / ΔT
Unit = JoC-1 or kJoC-1
what are the two methods for calibrating the calorimeter?
- Electrical calibration
- Chemical calibration
what is electrical calibration?
Electrical calibration involves filling the calorimeter with water (known vol/mass) and connecting it to a powerpack to create an electrical circuit through the water.
what equation is used to determine energy in electrical calibration?
q = V x I x t
q = J V = volts I = Amps t = sec
what else is measured in electrical calibration?
The ΔT that occurs as a result of the supplied energy is also measured. This allows the CF to be determined.
what is chemical calibration?
Chemical calibration involves selecting a reaction where the enthalpy change (heat of combustion) is well known (this is separate to the reaction/food you’re actually interested in).
how do you conduct chemical calibration?
- Place a known mass/moles of reactants in the calorimeter and use the known ΔH (heat of combustion) to identify how much energy (q) is being supplied to the calorimeter.
- This is done by cross multiplying to find what kJ (q) of energy has been supplied per mol/g of fuel.
- The ΔT that occurs as a result of this supplied energy is also measured. This allows the CF to be determined.
what do you need to record in a temp-time graph?
In addition to recording the max. temp obtained as a result of the supplied energy during calibration, the temp of the calorimeter is recorded for an additional 10-15 min AFTER calibration had been completed. This gives a more clear indication of how well the calorimeter retains heat.
what happens if you have a well insulated calorimeter according to the temp-time graph?
If you have a well insulated calorimeter, then the max. temp recorded can be used to identify ΔT and hence find CF.
what happens if you have a poor insulated calorimeter according to the temp-time graph?
If you have a poorly insulated calorimeter, the max. temp recorded can not be used to identify ΔT.
how do you get the ‘true’ value for the max temp with a poor insulated calorimeter?
- Use a line of best fit (downwards slope after turned off) along the data and extrapolate back to a point directly above the time when the current was turned on.
- This indicates what the max. temp recorded should have been.
- This “true” max. temp is what must be used to as ΔT and hence find CF.
- This backwards extrapolation accounts for the heat lost during the time the powerpack was on
steps bomb calorimetry for fuels after it has been calibrated?
- Bomb calorimetry used to find the energy of food/energy of flammable fuels.
- Remove any wires from calibration and add new water (same vol as used in calibration).
- Record the mass (g) or moles (mol) of fuel used (for foods as unknown usually g).
- Use ignition leads to light/combust the food and use thermometer to measure ΔT as a result of the foods combustion.
what is the equation for energy content in a calibrated calorimeter?
q = CF x ΔT
Unit = J or kJ depending on unit for CF
what happens if you need to find not the energy content but per mole/gram?
If not, use the fuels mass/moles and now known q to cross multiply and find kJg-1 or kJmol-1.
steps solution calorimetry for fuels after it has been calibrated?
- If solution calorimetry used, remove any wires from calibration and add new water (same vol as used in calibration).
- Record the mass (g) of reactants used. If formula is known this can be converted to moles.
- Add reactants to solution and use thermometer to measure ΔT as a result of the reaction.
how can energy content be determined by food labels?
- The type and amount each macromolecule within a food, as well as other key contents such as vitamins, fibre etc are listed on nutrition label of purchased foods.
- Nutrition labels often list a information per serving size and/or per 100g of food.
- Nutrition labels are listed in decreasing order according to mass.
- Allows for the mass to be multiplied by the energy content of macromolecules known in the data booklet.
for energy efficiency equations what units are used?
Can use either J or kJ as long as you are consistent top and bottom of equation.
what is the combustion reaction?
fuel + oxygen —> carbon dioxide + water + energy
what is the catalyst for a combustion reaction?
a spark
what bonds require more activation energy?
double bonds
what is the calibration factor for a good calorimeter?
lower
what is the calibration factor for a bad calorimeter?
higher
how do you get the enthalpy change from Hess’s law?
sum manipulated equation together to get the desired one
photosynthesis equation
6CO2(g) + 6H2O(l) + energy → C6H12O6(aq) + 6O2(g)
photosynthesis definition
The chemical process by which plants use sunlight, water and carbon dioxide to create oxygen and energy in the form of sugar.
what type of reaction is photosynthesis and why?
Endothermic, as it absorbs sunlight energy
conversion of energy in photosynthesis?
converts light energy from the sunlight (red & blue waves) to chemical energy in the form of sugar (glucose)
location of photosynthesis?
- occurs in the chloroplast of plants where they absorb sunlight
- stomata is whee carbon dioxide enters and leaves
- carbon dioxide and oxygen are transported by the xylem
- phloem transports glucose
definition of cellular respiration
Series of chemical equations that break down glucose to produce energy (ATP).
what type of reaction is cellular respiration and why?
Exothermic as organism produces energy
energy conversion in cellular respiration
releases energy from glucose, releases chemical energy
location of cellular respiration
- occurs in the mitochondria
- the circulatory system transports oxygen from lungs to cells and glucose via blood (xylem and phloem in plants)
what are types of factors to consider with fuels?
- environmental considerations (sourcing & products)
- toxins (people)
- safety
- economic (financeable viability)
what is the catalyst for photosynthesis?
sunlight/UV light
equation of fermentation of glucose to form bioethanol
C6H12O6(aq) –yeast-> 2C2H5OH(aq) + 2CO2(g) (fractional distillation needed for aq)
equation of complete combustion of ethanol
C2H5OH(l) + 3O2(g) —> 2CO2(g) + 3H20(g/l)
differences between biofuels and fossil fuels?
While biofuels are renewable, fossil fuels are non-renewable. The sources of biofuel are plant grains and organic residues. In contrast, the sources of fossil fuels are millions of year-old dead organisms.
types of fossil fuels?
coal, natural gas, petrol
types of biofuels?
biogas, bioethanol, biodiesel
what happens in the combustion reaction when there is not sufficient oxygen?
the carbon dioxide becomes carbon monoxide and then carbon (soot)
define limiting reactant
The reactant will completely react, according to the stoichiometric mole ratio. None of this reactant will be unreacted (left over) at the end of the reaction.
define excess reactant
The reactant that we have too much of, according to the stoichiometric mole ratio in the balanced equation. Some of this reactant will be unreacted (left over) at the end of the reaction
how is biodiesel produced?
Animal fats and vegetable oils contain triglycerides which react with alcohols in the presence of
potassium hydroxide (KOH) to produce glycerol and a mixture of fatty acid methyl esters known as
biodiesel. (transesterification reaction)
how is ethanol produced?
From the hydration of ethene from crude oil. Ethanol is made by ethene reacting with steam at a temperature of 300°C and pressure of around 60 to 70 atmospheres.
is ethanol a mixture?
Yes it is not a mixture as it goes through a refining/purification process, it might to to go through purification of removing water although,
distillation.
advantages of ethanol?
- There are no waste products.
- Doesn’t take up land with crops that could be used as food.
- Extracting is fast and reliable.
- More pure than bioethanol
disadvantages of ethanol?
- Ethene from crude oil which is a non-renewable resource
- The mining process of crude oil is bad for environment
how is bioethanol produced?
Via fermentation. Microbial fermentation is a natural process used to break larger organic molecules into simpler ones.
is bioethanol a mixture?
Bioethanol is a mixture as in the equation the ethanol is dissolved in a solution with water.
what second step has to happen to bioethanol?
For the bioethanol to be used the water must be stripped from the mixture to transform energy. The refining process includes stripping the water from the bioethanol product to be used for energy through distillation.
advantage of bioethanol?
Bioethanol is environmentally friendly as it is relatively carbon neutral as it is a renewable energy fuel
disadvantage of bioethanol?
- Transport however does contribute to the release of carbon dioxide
- Contributes to deforestation and habitat destruction
- Also contributes to food insecurity if grown from crop, growing for fuel instead
how is natural gas formed?
Natural gas is formed from the remains of plants and animal materials, when layers of decomposing plants and animals are subject to intense heat from the Earth and pressure from rocks.
how is natural gas sourced?
It is found in deposits in the Earth’s crust and can be accessed by drilling. It is then extracted from coal and shale deposits by a process known as fracking.
what is fracking?
Fracking involves injecting liquid at high pressure into coal and shale rocks to force open fissures (cracks) to extract the gas.
is natural gas a mixture?
Natural gas is a mixture of gases, it does go through a refining process where additional gases are removed through cryogenic expansion, where a powerful fan blows cooled gas from a narrow pipe into an expansion chamber. Water is also stripped from the natural gas in the purification process.
advantages of natural gas?
- natural gas is a relatively clean-burning fossil fuel, it contributes less than ethane to the environment negatively, releases less emissions
disadvantages of natural gas?
- Materials used for fracking have harmful impacts on the surrounding environment as well as water supplies.
- Is a non renewable source, meaning that the supply will eventually run out if we keep using it at this rate.
- When burned it releases methane which contributes to the enhanced greenhouse effect and warms the earth
- Also contributes to air and water pollution
how is biogas produced?
Biogas is produced by food or animal waste being broken down by microorganisms due to the lack of oxygen. This process is called anaerobic digestion. After this process, methane (CH4), CO2 and a other gases are released which makes up the biogas.
is biogas a mixture?
Biogas is a mixture of methane, CO2 and small portions of other gases. Biogas also goes through a purification process. To get rid of unwanted gases which may be CO2.
advantages of biogas?
Biogas is renewable and is made from food/amimal waste which means it can be replenished.
disadvantages of biogas?
- Biogas is flammable, highly toxic, and potentially explosive.
- Harmful compounds and air contaminants are released into the environment during production
- Burning manure-produced gas emits the same air contaminants as the combustion of fossil fuels.
- Factory farms that produce the biomethane can emit harmful pollutants into the air and discharge nitrates into groundwater.
- may contain harmful inorganic and organic components and exposure to these can result in serious health effects
what are macromolecules made up of?
Marcomolecules made made from smaller monomers into larger molecules such as polymers (in the case of carbohydrates and proteins). Or large molecules, but not polymers, made from smaller building blocks (as in the case with lipids/triglycerides).
Smallest component of carbohydrate?
Monosaccharides such as glucose are the smallest unit of carbohydrates (sugar).
Smallest component of protein?
Proteins consist of many amino acids bonded together.
Smallest component of fats?
Glycerol and fatty acids.
Main functional groups in carbohydrates?
- Carbonyl groups
- Hydroxyl groups
Main functional groups in proteins?
- Amino group
- hydrogen group
- carboxyl group
- R/sidechain group
Main functional groups in fats?
Ester
can the smaller monomers/units of the macromolecules undergo oxidisation?
yes all can, but carbohydrates more often
Name of reaction to synthesise the macromolecules?
Condensation reaction
Name of reaction to break down the macromolecules?
Hydrolysis
how is diesel produced?
It is produced by the fractional distillation of crude oil between 200 and 350 °C (392 and 662 °F) at atmospheric pressure, resulting in a mixture of carbon chains that typically contain between 9 and 25 carbon atoms per molecule
is biodiesel a mixture?
Biodiesel is the alcohol esters of the mixture of fatty acids.
is diesel a mixture?
Diesel oil is a complex mixture produced by the distillation of crude oil.
disadvantages of biodiesel?
- land and water resource requirements
- air and ground water pollution
- expensive
advantages of biodiesel?
- non toxic
- biodegardable
disadvantages of diesel?
- Emissions from diesel engines contribute to the production of ground-level ozone which damages crops, trees and other vegetation
advantages of diesel?
- more fuel efficient than petrol
functional groups of biodiesel?
- ester groups
- R group (carbon chains)
how is coal produced?
from wood and plant material decomposing over many many years
what determines how much energy coal contains?
The amount of water within the coal determines how much energy potential it has. Black coal, which contains a very small amount of water, has a high carbon content and a high amount of potential energy (as hydrogen and oxygen decreases and carbon increases).
how is crude oil (petrol) produced?
Crude oil (petroleum) is a mixture of hydrocarbon molecules that are mostly alkanes. Needs to be separated via fractional distillation to extract the smaller fractions which do serve as fuels.
what is natural gas composed of?
It is mainly composed of methane (CH4), with some small amounts of ethane (C2H6), propane (C3H8), water, sulphur, nitrogen and carbon dioxide present.
three main purposes of food for the body?
- Food supplies energy for our bodies.
- Food provides materials for the growth and repair of tissues.
- Food provides materials for the control of body processes.
