Accuracy, Precision, and Experimental Errors

Accuracy and Precision

• Accuracy measures how close values are to the true value.
• Measurement error is the difference between the true value and measured value.
• Precision measures how close experimental values are to each other.
• To be most accurate, equipment should be designed for the specific experimental purpose.

Repeatability and Reproducibility

• Repeatability is the closeness in results when a test is performed with the same equipment and person.
• Reproducibility involves a different person conducting the experiment with different tools and equipment but getting the same results.
• Reliability is the consistency of results when repeated multiple times; high repeatability and reproducibility indicate high reliability.
• Validity refers to whether the experiment checks against its hypothesis by either supporting or refuting it, and requires controlled variables.
• A test is valid if it's reliable.

Errors in Experiments

• Errors cause differences between experimental and theoretical values.
• Uncertainty is personal doubt in an experimental calculation.
• Personal errors are uncontrollable mistakes without a pattern, easily repeated and can be fixed by repeating the experiment.
• Systematic errors affect measurement accuracy, are consistent, and cannot be fixed by repeating; caused by faulty calibration or poorly maintained instruments.
• Random errors affect measurement precision and result in a wide spread of readings; machines can reduce human errors.

Fuels: Definition and Types

• A fuel is a substance that releases energy relatively quickly.
• Fossil fuels are non-renewable, from decomposing plant and animal matter over long periods.
• Biofuels are renewable and made from decomposing plant/animal and organic matter.
• Renewability refers to a resource's ability to be replaced by natural processes within a relatively short time.

Fossil Fuels: Coal, Natural Gas, and Petrol

• Coal is a fossil fuel from decomposing ancient plant materials buried for a long time.
• Coal changes from peat (lower carbon, higher water) to brown coal (higher carbon, lower water) to black coal (highest carbon, lowest water).
• Natural gas is obtained from Earth's crust deposits, mainly methane and other hydrocarbons, considered coal seam gas when extracted with coal.
• Petrol is a fossil fuel from crude oil (petroleum), containing primarily octane and other alkanes.
• Crude oil is separated into components via fractional distillation based on boiling points as per OCTANE FORMULA 2C8H|8(1) + 2502(g) → 16CO2(g) + 18H2O(1)

Biofuels: Biogas and Bioethanol

• Biogas is from the breakdown of organic matter by anaerobic enzymes, primarily methane (CH4).
• Bioethanol is made by fermentation where ethanol is produced, from biomass that may undergo hydrolysis.

Biodiesel and Carbon Neutrality

• Biodiesel is made through transesterification, mixing lipids (fats/oils) with methanol to form a glycerol molecule and biodiesel.
• Biofuels are considered carbon neutral because the carbon released equals the carbon absorbed.
• E10 is a mix of 10% bioethanol and 90% petrol, renewable, reduces CO2 emissions & compatible with many vehicles but has lower energy density.

Advantages and Disadvantages of Fuels

• Biofuels are renewable and carbon neutral.
• Biofuels have less energy content and have lower energy densities
• Fossil fuels have higher energy content and more energy density.
• Fossil fuels are not carbon neutral and non renewable.

Fuel Sources for the Body

• Fuel sources for the body are measured in kJ g-1 and are carbs, proteins and lipids.

Carbohydrates

• Carbohydrates are carbon, hydrogen & oxygen with the most abundant energy that converts easily to glucose.
• Carbs digest and break down (enzymes), absorb in the blood stream & undergo cellular respiration with oxygen to release energy
• Starch, a common carbohydrate in plants for storage, is a glucose monomer polymer that releases glucose when digested.

Proteins and Lipids

• Proteins are usually for growth and repair not commonly used for energy.
• Proteins are digested and broken into amino acids where nitrogen is removed. the carbon converts into glucose if fats/carbs aren't available.
• Lipids are triglycerides, more energy dense than carbs/proteins & used for long-term storage since don't mix with water, digest to produce CO2 and water.
• Fuel sources are measured in KJ g to indicate how much energy is released per gram of food.

Photosynthesis

• Photosynthesis converts light energy into chemical energy and is a source of glucose and oxygen for respiration with the formula 6CO2(g) + 6H2O(I) → C6H12O6(aq)+ 6O2(g).
• Since glucose is important for providing energy, this process creates glucose.
• Photosynthesis is endothermic, occurs in chloroplasts using sunlight, carbon dioxide, and water to produce glucose and oxygen for energy.

Oxidation and Cellular Respiration

• Oxidation of glucose serves as the primary carbohydrate energy source, balanced by C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(I).
• Cellular respiration is exothermic: energy is produced through aerobic/anaerobic respiration into carbon dioxide and water.
• Glucose is oxidized to carbon dioxide and loses electrons, while oxygen is reduced to water and gains electrons.

Bioethanol Production

• Bioethanol is produced by the fermentation of glucose and subsequent distillation for a more sustainable transport fuel with the formula of C6H12O6(aq) → 2C2H5OH(aq) + 2CO2(g).
• Glucose, a sugar found in plant materials, acts as the substrate for fermentation.
• Fermentation occurs without oxygen, where enzymes convert glucose into alcohol at 35°C.
• Carbohydrates blend with water + enzymes to break molecules into glucose through hydrolysis.
• Fermentation of glucose produces ethanol through anaerobic respiration.
• Distillation removes impurities and concentrates ethanol because as heating begins ethanol has a lower boiling point than water vaporizing it which is then collected.

Exothermic and Endothermic Reactions

• Exothermic reaction are defined as reactions that release energy into the environment leading to an increase on temperature
• Endothermic reactions are defined as reactions that absorb energy from the environment leading to a decrease in temperature.

Enthalpy Changes

• Enthalpy change is the total chemical energy change in a reaction, indicating heat absorbed or released, measured overall but not per unit of substance (H, in kj).
• Molar enthalpy change is the enthalpy change per mole of a substance (kj mol), e.g., 100kj released by 2 moles has an enthalpy change of 100/2=50kj.
• Enthalpy change for mixtures is measured in kj g, dealing with solutions or mixtures instead of pure substances (energy released per gram).
• Need to add reactants and products to the respective sides of chemical energy change diagrams.

Exothermic vs Endothermic Reactions

• Exothermic reactions release energy into the environment, increasing temperature. Reactant enthalpy exceeds product enthalpy due to bond-making releasing more energy than bond-breaking absorbs. Enthalpy value is negative.
• Endothermic reactions absorb energy from the environment, decreasing temperature. Product enthalpy exceeds reactant enthalpy as energy to break bonds (reactants) is more than bond-making (products). Enthalpy is positive (+).

Limiting Reactants and Reagents

• A limiting reagent is a substance completely used up in a reaction, preventing further product formation.
• The excess reactant remains after the reaction because not all of it reacted.
• The balanced equation is - 2H2 +O2 = 2H20 in order to calculate moles

Combustion Reactions

• Complete combustion is a chemical reaction where fuel reacts with enough oxygen to produce carbon dioxide and water, always exothermic as energy is released.
• Incomplete combustion occurs with insufficient oxygen, fuel doesnt fully oxidize and CO or carbon forms soot along with water, it has less energy requiring more fuel and can damage engines.

Balancing Combustion Equations

• Writing the equation requires including state symbols for the complete combustion of butane (C4H10).
• You need to add oxygen as a reactant and carbon dioxide and water as the products.
• Ensure you balance the carbon and the hydrogen atoms as well
• Write the equation, including state symbols, for the complete combustion of liquid ethanol (C2H5OH) in order to follow steps
• Add oxygen as a reactant and carbon dioxide and water as the products.
• Ensure you balance the carbon and the hydrogen atoms as well
• Energy released can be specified with a certain amount of fuel

Calculating Energy Released

• Calculate the quantity of energy released: requires you to Calculate the number of moles of the compound
• Thermochemically, if the moles changes,the enthalpy will change as well for example ch2+02= 20kj of energy so 2ch2+2o2= 40kj of energy
• If the equation is reversed, the sign infront of the enthalpy will change from positive to negative, or negative to positive
• More energy is absorbed when a water is liquid as the condensation process released extra heat
• Less energy is absorbed when water is a gas as it becomes a greenhouse gas.

Application of Stoichiometry

• Calculations relate to stoichiometry applications in combustion, including mass-mass, mass-volume/volume-volume stoichiometry for heat energy released, reactant and product amounts & greenhouse gas volume/mass like CO2, CH4 & H2O which are limited to standard lab at 25 °C and 100 kPa
• Stoichiometry studies moles & ratios in chemical reactions & rearranges existing atoms to know how much reactant, also the mass is the same between reactants and products
• CH4 + 2O2= CO2 and 2H20→ 1 mol of ch4, 2 mols of o2 create 1 mol of co2 and 2mol of h20 involves mass to mass calculations

Mass-Volume Stoichiometry

• For standard lab conditions, use the formula n=V/Vm
• For non-standard, use pv=nRt
• Since all gases occupy the same volume measured at the same temperature and pressure, the mol ratio equals the volume ratio.

Combustion and Energy

• Energy depends on fuel type, fuel amount, and complete vs. incomplete combustion.
• Complete fuel combustion releases more energy.
• Greenhouse gas can absorb infrared radiation
• Greenhouse gases produced by combustion is Carbon dioxide and water (in gaseous form) as-well as methane

Methane

• Methane is the most potent gas.
• This is dependent upon the volume of each greenhouse gases.
• Essentially, in a chemical reaction, the mol ratio wont be correct and rightly adjusted so one reactant will be completely used up and one reactant will be left in excess

Reactants

• Limiting reactant is the reactant that is completely consumed in the reaction
• The excess reactant is the reactant that is left over
• The amount of limiting reactant must always be used to determine the amount of product formed
• To calculate limiting reactant, first find the moles of each reactant, then use the mol ratio of any reactant to find how much of that reactant is needed to find the other reactant. The number which is less is the limiting reactant

Using Specific Heat Capacity

• it's purpose is to determine ideal fuel
• Water’s specific heat capacity: energy in joules to increase a specific amount of water (1 gram) by 1*C and is energy that is stored
• It's measured in JgC* and is c
• A substance's Specific heat capacity indicates its bond types
• For example, water with hydrogen bonds has higher Specific heat capacity and requires more energy to break
• Substances with lower SHC warm faster as they need less energy to increase the temperature
• Heat energy transfer is measured by Q=mcat (at- change in temperature)
• Q is measured in Joules
• For questions about mass in liters, the density of water is 1,0g ML so 1g=1L

Experimental Heat Determination

• Experimentally, pure substance combustion occurs under a water container; heat is transferred to the water.
• Organic liquids (alcohols & alkanes) usually used for large energy release
• The key information includes the mass of water, the temperature changes that indicate water energy absorption) & organic fuel mass.
• Heat of combustion (energy emitted) is calculated by H=q/n
• q being the energy absorbed by water
• n is the number of fuel amount that has been burnt

Variations in Values

• The experiment assumes all energy is transferred to the water
• Possible Heat loss where water will not increase as much due to this
• Ways to prevent this is by insulating the beaker of water and putting a lid on the container
• Incomplete combustion can occur, reducing total energy released where fuel doesn't react as much

Energy Content of Food, Measuring Energy Change

• Energy content =q/m where m is the change in mass of the food
• Energy content is measured in kj per gram as some fuels and food are mixtured and not pure substances
• Heat loss is a major problem so the values are always less than the theoretical values
• Calorimetry measures heat energy change in chemical reactions (like fuel combustion).
• Calorimeters measure energy changes that occur from heat reaction
• Calorimeters are designed that minimize energy loss, transferring most to the water volume.

Solution Calorimeters

• Solution calorimeter measures solution energy changes (aq), like a lidded polystyrene foam cup.
• Polystyrene's insulation prevents heat loss, maxing water transfer. However the foam absorbs some heat, so change in temp will be lower
• all initial data is measured such as the volume of water, initial temp and amount of reactant used
• Water temp increases, the reaction is exothermic because heat energy is released
• Temp decreases, then the reaction is endothermic
• SOLUTION calorimeters cannot determine fuel gas content as they need oxygen for burning.
• They are used for aqueous such as acids, bases, metals and acids and solids with water
• Use a stirrer to ensure uniform water temp because inaccurate temps occur otherwise

Accurate Calibration Measurements

• For more precise measurements, know the calibration factor (energy to raise temp by 1*C for calorimeter).
• Once known, calibrate.
• Electrical calibration can be use and can be represented by formula, E(energy)= Volts x amps x Time
• CF= E/T(change in temp) = Vit/T

Temperature Time Measurements

• If the calorimeter is not insulated well enough, the temperature cannot simply be final-initial as it will slowly lose heat during and after the heater is operating
• A graph with perfect insulation is a straight constant line where no extrapolation is needed
• Imperfect calibration requires extrapolation.
• Solution calorimetry calibrates by performing a chemical reaction for a known thermal energy (H) and then measuring the temperature rise
• Dissolve the substance in the calorimeter and measure temp change for calibration.
• E=nxH -- CF=E/T
• Food supplies the energy required for chemical reactions that occur in the body
• Energy can be transformed into one form or another for example, energy can be lost due to mechanical energy for cyclists

Transformed Amounts of Reactions

• The total amount of energy is unchanged, however not all energy will be transformed into the form needed
• Energy Efficiency is the percentage of energy from a source that is converted into either useful or required energy
• Ex- petrol that combusts will form thermal energy, some of it propels the car, other thermal energy goes to other processes.
• Energy efficiency = Useful transfer/energy input x100
• Useful energy is the amount transferred successfully
• the max energy efficiency is 100% but it cannot be used as energy is aiways lost

Energy in Food

• the core nutrients are carbohydrates, proteins and fats-
• energy released when food is burned is greater than the energy available to humans due to incomplete combustion
• the energy can vary . in carbs, the energy can vary
• humans don't have cellulose so no energy is absorbed