3.2.2 Kinetics. Effect of Concentration. 135 minutes. 134 marks. Page 1 of 13

Transcription

1 3.. Kinetics Effect of Concentration 35 minutes 34 marks Page of 3

2 M. (a) Activation energy;- The minimum energy needed for a reaction to occur / start () Catalyst effect:- Alternative route (or more molecules have Ea) () Lower activation energy () (c) Increase in moles of gas:- Position of E mp unchanged () More molecules with E mp () Area under curve increases () Molecules with E E a increased () Temperature decreased:- Position of E mp moves to the left () More molecules with E mp () Area under curve unchanged () Molecules with E E a decreased () Catalyst introduced:- Position of E mp unchanged () Molecules with E mp unchanged () Area under curve unchanged () Molecules with E E a increased () [5] M. (a) Increase in temperature: Yield is increased (Allow if for H (g) or products) () Reaction endothermic () Equilibrium moves to the right forward, Equilibrium moves to oppose change to absorb heat () If Yield statement incorrect allow max one if reaction stated to be endothermic Increase in pressure: Yield is decreased (Allow if for H (g) or products) () Increase in moles of gas or moles increased to 4 moles or more moles on right () Equilibrium moves to the left backwards, Equilibrium moves to oppose change to reduce pressure () If Yield statement incorrect allow max one if number of moles change is correct. 6 Page of 3

3 Equilibrium yield: Unaffected or equilibrium unchanged () Rate or speed increased () Forward and backwards reactions equally or by the same amount () Amount of hydrogen produced: More hydrogen produced () 4 [0] M3. (a) minimum energy () required before a reaction can occur or go or start () speeds up (changes) reaction rate () without being (chemically) changed (used up) () (c) provides alternative reaction route () with a lower activation energy () in and (c) reward 4 marks for 4 points wherever found (d) (i) Page 3 of 3

4 (iii) fewer collisions () W used up () or reactants or reagents or fewer particles 6 [] M4. (a) (i) 4 (i) collide () with sufficient energy (or E E a ) () (or with correct orientation) molecules (or particles) have more energy (or move faster) () more molecules (or collisions) have E E a (or sufficient energy) () 4 (c) (i) equilibrium reached () (or rate forward reaction = rate backward) Reaction is endothermic () or ΔH +ve or reverse reaction is exothermic endothermic reaction favoured () (or reaction shifts to R or moves forward or more products formed) 3 [] Page 4 of 3

5 M5. (a) Graph starts at origin Graph skewed to left and has decreasing gradient to maximum Graph after maximum decreases in steepness, never touches x axis, levels out less than 5 mm from x axis. Minimum energy To start a reaction (or for a reaction to occur) (c) Molecules gain energy (or always some molecules have E > E a ) Due to collisions (d) Decreases E a lowered () By alternative route () So more molecules have energy > E a () max [0] M6. (a) Gradient (or slope) (or draw a tangent) (i) Curve X is lower and starts at origin And levels out at same volume as original curve Curve Y is steeper than original and starts at origin Then levels out at half the volume of the original Page 5 of 3

6 (c) (i) H O H O + O (iii) Speeds up (alters the rate of) a chemical reaction Remains unchanged (or not used up) Remains unchanged (or not used up or not in the overall reaction equation) Offers alternative reaction route (or acts as an intermediate) [0] M7. (a) the minimum energy; Energy required for a reaction to occur; (or to start a reaction or for successful collisions) axes labelled:- y: number (or fraction or %) of molecules (or particles) x: energy (or KE); curve starts at origin; skewed to right; approaches x axis as an asymptote; (penalise a curve that levels off > 0% of max peak height or a curve that crosses the energy axis) second curve displaced to the left (and does not cross T curve for a second time) and peak higher; many fewer molecules; fewer molecules have E > E a ; (can score this mark from suitably marked curves) Page 6 of 3

7 (c) molecules (or particles or collisions) do not have enough energy; (or orientation may be wrong) increase the pressure; (or increase the concentration or reduce the volume) increases the collision frequency; (or more collisions) (do not allow if stated to be due to increase in energy implied by temperature increase) add a catalyst; lowers activation energy (or E a ) (Q of L mark); [5] M8. (a) minimum energy to start a reaction/ for a reaction to occur/ for a successful collision activation energy is high / few molecules/particles have sufficient energy to react/few molecules/particles have the required activation energy (or breaking bonds needs much energy) (c) molecules are closer together/ more particles in a given volume therefore collide more often (d) many more molecules have energy greater than activation energy (QoL) (e) speeds up a reaction but is chemically unchanged at the end (f) increases the surface area [9] Page 7 of 3

8 M9. (a) Sulfur S S 8 Sulphur M The activation energy is the minimum / least / lowest Mark these independently M Energy for a reaction to occur / to go / to start Energy for a successful / effective collision (c) Explanation: M Twice as many / double number of particles M NOT molecules M More / twice / double (effective) collisions (in a given time) Double / greater / increased collision frequency (d) (i) (Measured) change in concentration (of a substance) in unit time / given time May be written mathematically the gradient of the concentration (against) time The measured change / amount (of precipitate) / cloudiness is fixed or constant or unchanged [7] M0. (a) M The activation energy is the minimum / least / lowest energy Mark independently Ignore heat and ignore enthalpy M (energy) for a reaction to occur / to go / to start (energy) for a successful / effective collision Ignore breaking the bonds M Catalysts provide an alternative route an alternative mechanism alternative / different path(way) M Lowers the activation energy Mark independently Ignore reference to surface Page 8 of 3

9 (c) (i) Stay(s) the same (iii) (iv) Increases Credit increase or increased Increases Credit increase or increased Stay(s) the same (d) (i) M yeast or zymase M ethanol Ignore enzyme In M, ignore alcohol and ignore any formula M (Concentrated) H 3 PO 4 (Concentrated) H SO 4 M butan--ol Credit correct names Ignore hydrogenphosphate or hydrogensulfate Ignore dilute or aq Do not penalise absence of hyphens in name. In M, ignore any formula [] M. (a) Award in either order for curve Steeper requires line to be on the left of the original line, starting from the origin M curve is steeper than original and starts at the origin M curve levels at the top line on the graph Award in either order for curve Shallower requires line to be on the right of the original line, starting from the origin M curve is shallower than original and starts at the origin M curve levels at the first line on the graph Page 9 of 3

10 (c) M curve would be steeper than original Steeper requires line to be on the left of the original line, starting from the origin M curve levels at the same original volume of O (d) M The (concentration / amount of) H O or reactant falls / decreases / used up Mark independently The number of H O or reactant molecules/ particles falls / decreases M The rate of reaction / rate of decomposition / rate of formation of oxygen / frequency of collisions / (effective) collisions in a given time decreases / is slower (e) (i) H O H O + O Ignore state symbols Accept only this equation or its multiples Extra species must be crossed through hydrogen bromide / it does not appear in the overall equation hydrogen bromide / it is not used up in the reaction / unchanged at the end of the reaction hydrogen bromide / it is regenerated / re-formed (in Step ) [0] M. (a) (i) Change in concentration (of a substance / reactant / product) in unit time / given time / per (specified) unit of time This may be written mathematically may refer to the gradient of a graph of concentration / volume against time Amount of substance formed / used up in unit time / given time / per (specified) unit of time Ignore additional information including reference to collisions Page 0 of 3

11 At W M (QoL) The rate / it is zero M The magnesium has all reacted / has been used up Ignore reference to the acid being used up No more collisions possible between acid and Mg Reaction is complete / it has stopped No more hydrogen / product is produced (iii) M Twice / double as many particles / hydrogen ions (in a given volume) Penalise reference to (hydrochloric acid) molecules in M Penalise reference to HCl particles in M Twice / double as much hydrochloric acid M Twice / double as many effective / successful collisions (in a given time) Twice / double as many collisions with either sufficient energy to react with E E a double the successful / effective collision frequency (i) The activation energy is the minimum energy for a reaction to go / start Minimum energy for a successful/ effective collision Page of 3

12 M Products lower than reactants on the profile Mark independently M Activation energy (E a ) shown and labelled correctly from reactants to peak of curve Mark independently (c) (i) Ba + H O Ba + H O Ba(OH) + H Ba + + OH + H Allow multiples Ignore state symbols M Ba + + SO 4 BaSO 4 M Ignore state symbols in M Not multiples in M White precipitate / solid Extra ions must be cancelled Penalise contradictory observations in M (iii) M Barium meal / barium swallow / barium enema Accept a correct reference to M written in the explanation in M, unless contradictory M used in X-rays to block X-rays X-ray contrast medium CT scans BaSO 4 / barium sulfate is insoluble (and therefore not toxic) For M NOT barium ions NOT barium NOT barium meal and NOT It Ignore radio-tracing [3] Page of 3

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