# Chemistry Unit 4 flashcards

### Description

A2 level Chemistry (Unit 4) Flashcards on Chemistry Unit 4 flashcards, created by J000D97 on 02/27/2015.
Flashcards by J000D97, updated more than 1 year ago
 Created by J000D97 almost 8 years ago
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## Resource summary

 Question Answer What are the units of rate? mol/$$dm^3$$/s What are the units of k for a reaction of overall order 0 mol/$$dm^3$$/s What are the units of k for a reaction of overall order 1 /s What are the units of k for a reaction of overall order 2 $$dm^3$$/mol/s What are the units of k for a reaction of overall order 3 $$dm^6$$/$$mol^2$$/s Define half life The time taken for half a reactant to be used up in a reaction process What is the rate determining step? The slowest step in a multi-step reaction which decides the overall reaction rate and whose relevant reactants appear in the rate equation. Define activation energy The minimum energy requirement needed by reactants before products can form. What are the 3 stages that occur in catalytic converters? Reduction Oxidation Control system What occurs in the reduction stage of catalytic converters? Platinum and rhodium reduce nitrogen oxides emissions by removing O What occurs in the oxidation stage of catalytic converters? A platinum and palladium catalyst aid the reaction of unburnt HC's and CO with O to produce $$CO_2$$ and $$H_20$$. What occurs in the control system stage of catalytic converters? Lambda sensors and heated oxygen sensors monitor exhaust and the information is used to adjust fuel injection. It monitors the efficiency of the catalyst. List the 5 ways you can measure rates of reactions Gas volume Mass change Colorimetry Titimetric analysis Conductimetric analysis What are the 2 main factors involved in fermentation for production of beer? Start and maximum temperature What is the rate equation for the reaction between propanone and iodine? Rate=k[CH3COCH3][$$H^+$$] $$[I_2]^0$$ Radioactive decay is a ____ order reaction. 1st Describe the sequence of events occurring on a hetrogenous catalyst. Reactants are adsorbed onto the metal's surface at active sites This weakens bonds between atoms in reactant molecules and specifically orientates them. Activation energy is lowered An activated complex forms gradually as molecules are adsorbed. Product molecules form. Product molecules desorp and leave the metal's surface. What is the gas constant value and units? 8.314 J/K/mol How many molecules are involved in the RDS of an SN2 reaction? 2 How many molecules are involved in the RDS of an SN1 reaction? 1 Which types of halogenoalkanes do SN2 and which do SN1? Primary do SN2 Secondary do both Tertiary do SN1 Why can tertiary halogenoalkanes perform SN1 whereas primary do SN2? Tertiary halogenoalkanes have 3 electron pushing alkyl groups pushing towards the halogen which cause it to come off more easily and without the need for the nucleophile to bond first. It can form a more stable carbocation because of these alkyl groups. In which mechanism is a 5 bonded transition state formed? SN2 Is a carbocation formed in SN1 or SN2? SN1 Describe entropy A measure of disorder of a system What are the units of entropy? J/mol/K What has 0 entropy? A perfect crystal at OK. Describe a perfect crystal A constant fixed internal lattice with no rotating or vibrating particles with only one possible arrangement. If you increase the temperature of a substance why does its entropy increase even if it doesn't change state? Because you are increasing the energy of the particles therefore the higher the temperature the more quanta of energy a substance has and the more ways they can be distributed, which means higher entropy. In which direction does entropy go? up Is the entropy of a gas higher or lower than that of its corresponding solid? Higher Total S = ... S of systems + S of surroundings What happens to Kc as S total increases? And why? It increases because S total = RlnK S of system is... sum of S of products - sum of S of reactants S of surroundings is... $\frac{-ΔH}{T/K}$ When is a reaction spontaneous if: ΔS syst +ve ΔH +ve At high temperatures When is a reaction spontaneous if: ΔS syst +ve ΔH -ve Always When is a reaction spontaneous if: ΔS syst -ve ΔH +ve Never When is a reaction spontaneous if: ΔS syst -ve ΔH -ve Spontaneous at low temepratures What are the 2 formulas for ΔG? -T ΔStot ΔH-T ΔSsys Define: ΔH hydration The amount of energy released when 1 mole of gaseous ions dissolves in water under SC's to produce a 1M solution. Define: ΔH solution The ΔH when 1 mole of the compound dissolves in a stated amount of water under SC's. Define LE ΔH formation of 1 mole of ionic compound from gaseous ions under SC's or energy needed to break up one mole of the lattice. As ionic radii increases, LE... Decreases ΔH hydration = ... ΔH hyd [cation] + ΔH hyd [anion] ΔH solution = ... ∑ΔH hyd - ΔH LE How can you tell if a compound will dissolve in water? ΔH hyd > ΔH LE Under what conditions may a solid dissolve if ΔH hyd < ΔH LE? ΔH solution would be +ve so ΔS surr is -ve therefore ΔS syst mustbe +ve enough or temperature be high to keep ΔG -ve. Dynamic equilibria can only occur in a ________ container. Sealed At equilibrium do the concs of reactants and products have to be the same? NO What is the contact process reaction? 2$$SO_2$$ + $$O_2$$ <--> 2$$SO_3$$ State the Harber process reaction $$N_2$$ + 3$$H_2$$ <--> 2$$NH_3$$ How do you determine the equilibrium constant? By experiment Does increasing total pressure alter Kp? NO Does increasing temperature affect either of Kc or Kp? Both How do you find Kc for the reverse of the reaction you calculated it for? 1/Kc value Partial pressure formula Pp = moles/(tot moles at eq.) x P tot pP tot = ... p(A) + p(B) + ...... When a system is in dynamic equilibrium ΔS tot = ... 0 if Kc/Kp is almost 1... reactant and product concs are almost the same. If Kc/Kp is greater than $$10^{10}$$... The reaction has gone to completion. If Kc/Kp is less than $$10^{-10}$$... The reaction doesn't occur. If temperature increases how does this affect ΔS system? There is little change unless a reactant or product changes state. How is ΔS tot affected is temperature in decreased in an exo reaction? It decreases How is ΔS tot affected is temperature in decreased in an endo reaction? It increases How can atom economy be improved? By capturing and recycling unused reactants and using more efficient alternative reactions. Why is it important to control reactions? To produce adequate yields To keep it safe To keep the equilibrium economically viable What is the oxonium ion? $$H_3O^+$$ Kw = ... [OH-][H+] Ka = ... acid dissociation constant pKa=pH when... [A-]=[HA] For a strong acid a ___fold dilution increases pH by 1 10 Dilution causes proportion of dissociated weak acid to... increase What is the realtionship between Ka, Kb and Kw? Kw = Kb x Ka What are indicators? Weak acids or bases In the middle of an indicator's colour change what conc = what? and what does this mean? [HIn] = [$$In^-$$] pKIn = pH Strong base / weak acid indicator phenolphthalein Strong acid / weak base indicator Methyl orange or bromothymol blue Indicator for strong base / strong acid methyl orange bromothymol blue phenolphthalein Define buffer Something which resits small changes in pH due to the addition of $$H^+$$ or $$OH^-$$ In a buffer eq. conc of A- = (approx) initial conc added In a buffer solution eq. conc of acid = and why? (apporx) initial conc. as salt reservoir pushes eq. left so very little dissociates. At Veq/2... [HA] = [$$A^-$$] so pKa = pH Dimensions of vertical region on a titration curve 2.5$$cm^3$$ across 3-6 units long Do high protein foods have high or low buffer capacities and why? High B/c AA's have acidic and basic characteristics Describe stereoisomerism having the same group of atoms in different spatial arangements What are the 2 forms of optical isomers called? Laveo and dextro What type of light do optical isomers rotate? Plane-polarised monochromatic light EM radiation is a _____ wave transverse Describe monochromatic light Light of a single wavelength Solubility of Als and ketones? Patterns? small mols = miscible Decreases as chain length increases What happens when molecules absorb IR rad? The bonds vibrate by stretching and bending Only what molecules can absorb IR rad? Ones that can change their polarity as they vibrate. Describe how microwaves heat food Microwaves create an electric field which causes the water molecules to line up with it. The field switches directions and water molecules flip. Energy in microwaves is converted to thermal energy. Only _____ molecules can be heated by a microwave. Polar What does each peak represent in a low res nmr spectra? A different proton environment. Why does splitting occur in nmr? Due to interactions between protons on neighbouring atoms. What are the units of chemical shift? ppm What can you use IR for? Following progression of preactions What is the furthest right peak in a mass spec called? molecular ion peak Gas-liq chromatography stationary and mobile phase Stationary = liquid Mobile = inert gas HPLC - P stands for: Performance NOT pressure HPLC mobile and stationary phase Stationary = solid Mobile = liquid Define: retention time Time taken for a particular sample to travel to the detector, measured from injection to maximum peak on the display.

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