C7 Flashcards
Core parctical:investigating effects of changing conditions of a reaction on rates of a chemical reaction by:
a)measuring gas production.
b)observing a colour change.
a)-support a gas syringe with a stand, boss and clamp.
-add 50cm^3 of dilute HCL to conical flask.
-add 0.4g of calcium carbonate(marble chips) to flask. immediately connect gas syring and start stop clock.
-record time for every 10cm^3 gas produced.
-When reacftion complete, clean a pparatus.
-repeat with diff conces of HCL.
-total volume of gas produced/reaction time then compare with the mean of the results of each conc and describe effect increasing conc of acid on mean rate of reaction.
b)-add 50cm^3 of dilute sodium thiosulfate solution to conical flask.
-place flask on piece of paperwith balck cross drawn on it.
-use diff measuring cylinder and add 10cm^3 of dilute HCL to flask.
-immediately swirl the flask to mix and start a stop clock.
-measure and record temp of the reaction mixture.
-Look down through mixture and when cross no longer visible stop clock and record time.
-measure and record temp of mixture and clean apparatus.
-repeat starting with diff temps of sodium thiosulfate sol.
-1000/time for each temp to get reaction rate.
-rate of reaction increases as temp increases.
rate of reaction calc
1/time.
How reactions occur and when are they increased
-occur when particles collide and increased when the frequency/energy of collisions is increased.
effects of changing conditions of reaction rates
Temperature-if increased then rate of reaction is increased because reactant particles move faster, energy of particles increase, frequency of successful collisions between reactant particles increases, therefore rate increases, frequency of collisions increases, proportional of successful collisions increases.
Concentration/pressure(on reactions involving gases)-increased=reactant particles closer together, frequency of collisions increases, rate of reaction increases, mean energy does not change, frequency of successful collisions increase as well as overall frequency.
Surface area to volume ratio of a solid-large lumps have smaller ratios than smaller lumps or powders, if lump made into powder vol stays same but exposed surface area increases so ratio increases, if ration increased more reactant particles are exposed to the surface, frequency of collisions of reactant particles increases so rate of reaction increases too. Mean energy does not change but frequency of successful collisions does.
Interpretation of graphs of mass, volume or conc of reactant or product against time
-gradient of the line is equal to rate of reaction
-faster reaction/higher rate=steeper line,finishes sooner.
-time on x-axis.
What is a catalyst
-speeds up/increases rate of reaction
-without altering the products of the reaction
-is unchanged chemically
and in the mass at the end of the reaction
-do not affect yield of reaction
How do they work
-lowers the activation energy that is needed for the reaction to take place
-does not change the frequency of collisions but increases proportion of successful collisions because a greater proportion of collisions now exceeds this lower activation energy.
Enzymes
-biological catalysts
-allows some industrial reactions to happen at lower temps and pressures than normally needs
-yeast is a single-celled fungus
-enzymes in yeast are used to produce wine, beer and other alcoholic drinks by fermentation of sugars.
collision theory
-reactant particles must collide with each other
-particles must have enough energy for them to react(activation energy is the minimum amount of energy needed for a collision to be successful.
What reactions to changes in heat energy accompany
-salts dissolving in water
-neutralisation reactions
-displacement reactions
-precipitation reactions
when these reactions take place in solution, temp changes can be measured to reflect heat changes.
exothermic reaction
Heat energy is given out
endothermic reaction
heat energy is taken in
breaking and making of bonds
breaking-endothermic
making-exothermic
Overall heat energy change for a reaction=
exothermic if more heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants.
endothermic if less heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants.
Calculation for energy change in reactions
energy in(sum of all the bond energies for bonds broken in the reactants)-energy out(sum of all the bond energies for all the bonds formed in the products)=energy change(KJ mol^-1)
