Reactivity 1.1

• Actual yield tends to be lower than theoretical yield often due to residues and material errors that can make the experimented amount, however slightly, less than predicted
• When actual yield is greater than theoretically predicted, it is assumed to be from its impurities or environmental substances that have been added to the mixture
• Between two electronegative elements, the one with the smaller value will have a delta positive charge (is the positive dipole) while the one with the greater value will have a delta negative charge (is the negative dipole)
• To find the amount of a reactant (B) needed to react with a given amount of the other reactant (A)

  (coefficient of B/coefficient of A) x (given moles of A/1) = moles of B needed
• Using limiting reactant to find product

  moles of reactant: given mass/its molecular mass

  moles needed: moles of reactant x (coefficient of product/coefficient of reactant)

  mass needed: moles needed x molecular mass of product
• Combustion analysis

  Using product mass (given) to identify unknown molecular formula of a hydro-carbon by finding the moles of hydrogen in water and moles of carbon in carbon dioxide, then dividing them by the smallest value found to find the formula (multiply to whole numbers, if needed).

  
• To calculate total pressure of a vessel when two different vessels are open and mixed, use Boyle's Law to find the partial pressure of each- assuming the volume of the mixed solution is the sum of the two separate gases- and then add them together.
• Calorimetry -> q=mcΔT
• Bond Enthalpy refers to the energy needed to break bonds
• How do you measure enthalpy change Sum of bond enthalpies of bonds broken (reactants) minus sum of bond enthalpies of bonds formed (products) ΣBer - ΣBep = ΔH
• What is enthalpy initial heat energy stored in reactants
• Why do we measure enthalpy change? Because absolute enthalpy values cannot be strictly known so enthalpy change is calculated instead
• What does a negetive enthalpy change tell us about the reaction? It is exothermic, meaning that the reaction loses energy to its surroundings to make the products more stable than the reactants
• What does a positive enthalpy tell us about the reaction? The reaction is endothermic which means it absorbes energy from its surroundings to create a product which is more unstable than its reactants
• What is standard enthalpy change (ΔH°)? The enthalpy change of a reaction under standard conditions (1atm and 298K). This is signified by the ° symbol.
• Difference between open and closed systems Open systems exchange energy and matter with its surroundings while closed systems only exchange energy
• What does temperature depend on and what form of temperature is usually used in chemistry Temperature depends on mass and nature (specific heat capacity) or the molecule/substance. It is usually measured in Kelvins in chemistry as Kelvins are a direct measure of ave. kinetic energy.
• Exothermic reaction equation + labeled diagram A + B = C + energy [diagram tba]
• Endothermic reaction equation + labeled diagram A + B + energy = C [diagram tba]
• Law of Conservation Energy Energy cannot be created or destroyed in a closed system- it can only be transformed or transfered from one form to another
• 3 types of energy transfers conduction --> irect contact convention --> movement of fluids radiation --> electromagnetic waves
• Specific Heat Capacity equation Q = mcΔT heat added = mass x specific heat capacity x change in temperature (in either K or C°)
• What is specific heat capacity? The heat needed to be added to increase the temp of 1 grams of a substance by 1K or 1°C
• What is Entropy? State/degree of disorder in a reaction.
• How to, without any calculation, estimate sign of entropy (positive or negetive)? Usually increased disorder is seen with increased amounts of gas molecules in an equation. If the products side has more gas molecules, entropy can be expected to be positive. If the reactants have more gas molecules, entropy will be negetive, as there is less disorder in the final product, therefore the reaction loses disorder.
• Equation to measure change in entropy Sum of entropy of products subtracted by the sum of entropy of reactants Σ PS° - Σ RS° = ΔS°
• 5 examples of Exothermic equations Combustion Neutralization Freezing (liquid --> solid) Condensation (gas --> liquid) Deposition (gas ---> solid)
• 5 examples of Endothermic reactions Photosynthesis Thermal decomposition Melting (solid --> liquid) Evaporation/boiling (liquid --> gas) Sublimation (solid --> gas)
• What is standard bond enthaply? "The quantity of energy needs to break 1 mol of bonds in gaseous state under standard conditions (1atm + 298K). Also called ""Dissociation energy"""
• What data would you require to solve for the enthalpy of reaction using Hess’s law for the following: 3C(s) + 3H2(g) → CH2=CHCH3(g) Standard enthalpy of combustion (used as the reaction is a formation reaction)
• Define standard enthalpy change of combustion Also called the molar enthalpy of combustion, it is the change in enthalpy when 1 mol of a substance is burned completely in oxygen under standard conditions (298K, 100kPa)
• Define standard enthalpy of formation Also called the molar enthalpy of formation, it is the energy change when 1 mol of a substance is formed from their seperate elements in standard states
• What can the standard enthalpy of combustion and formation tell us? The stability and possibility for a reaction to occur (for scientists), or, more pratically, the calories present in food or the efficency of fuels
• How is standard enthalpy of combustion calculated? ΔH = ΣΔHf (products) - ΣΔHf (reactants)
• How is the standard enthalpy of formation calculated? ΔH = ΣΔHc (reactants) - ΣΔHc (products)
• Describe the steps of the Born-Haber Cycle and the enthalpies accosiated with them 1. Molecules are turned to their gaseous states (ΔHat: Enthalpy of atomisation) 2. Electrons are removed from metals to form cations (ΔHIE: Enthalpy of ionization energy) 3. Bonds are broken in non-metals (BE: Bond energy) 4. Electrons are added to non-metals to form anions (ΔHEA: Enthalpy of electron affinitiy)
• Write the equation to find Lattice Enthalpy with the Born-Haber cycle ΔHlattice=ΔHat+BE+ΔHIE+ΔHEA-ΔHf (lattice enthalpy = atomization enthalpy + bond energy + ionization energy + electron affinity - formation enthalpy)
• Does the Born-Haber Cycle calculate theroretical or experimental values for lattic enthalpy and why? Experimental values as the actualy experiements are often dangerous to do.
• Define bond enthalpy "Energy needed to break 1 mol of a bond in gaseous state. Also called ""bond dissasociation energy"""
• "Determine the type of reaction that follows bonds ""forming""" Exothermic reactions where energy is released to create a stable product. ex. 2F --> F2