rate of reaction

in which ways are rate of reaction measured

how fast a product is made

how fast a reactant is used up

what are the 3 solutions used to determine the rate of reaction

mass loss, gas collection and precipitation

mass loss

measuring the mass loss in the reactants over time

gas collection

measuring the amount of gas formed over time

precipitation

measure the formation of a precipitate over time

what are the 2 equations for calculating the rate

rate=amount of reactant used/time taken

or

rate=amount of product made/time taken

whats the measurement for rate

either g/s or cm³ /s or dm³ /s or mol/s

mass loss method

the mass is measure every few seconds and the change in mass over time is recorded as the gas escapes

the reaction is typically performed in a conical flask placed on top of a balance to measure the loss in mass

however one limitation is that the gas must be sufficiently dense or the change in mass is too small to measure

gas collection method

the volume of gas produced ovee time is recorded

one gas collection setup involves collecting a gas through water using an inverted measuring cylinder

although, the gas can be captured in a gas syringe which measures its volume

precipitation method

participation reaction forms a solid precipitate when 2 clear solutions are mixed together

the precipitate clouds the reaction mix so if the flask is placed over a piece of paper with a cross on it, the time it takes for the cross to disappear from view is measured

this method can be subjective

what is the equation to find out moles per unit time

mole per unit time= mass per unit time/molar mass of the substance

initial rate graph for product

an initial rate graph for the formation of a product shows a straight line with a positive correlation starting from the origin

initial rate graph for reactant

an initial rate graph for a reactant shows a straight line with a negative correlation starting from the y axis

calculation for the mean rate of reaction

taking the difference between 2 points on the curve

what 4 factors affect the rate of reaction

the concentration of the reactants in solution or the pressure of reacting gases

the temp of the reaction

surface area of solid reactants

the presence of a catalyst

required practical: investigating effect of concentration on rate of reaction (measuring turbidity) objective

to investigate the effect of changing conc on the rate of reaction by measuring the formation of the precipitate

required practical: investigating effect of concentration on rate of reaction (measuring turbidity) hypothesis

a precipitate will be formed quicker of the reactants is greater

required practical: investigating effect of concentration on rate of reaction (measuring turbidity) materials

40g/dm³ sodium thiosulfate solution

1.0mol/dm3 dilute hydrochloric acid

conical flask

black cross on paper

white paper or white tile

stop watch or timer

required practical: investigating effect of concentration on rate of reaction (measuring turbidity) method

1. measure 50cm3 of NA₂S₂O₃ solution into a flask

2. measure 5cm² of dilute HCL into a measuring cylinder

3. draw a dark cross on a piece of paper and put it underneath the flask

4. add the acid into the flask and immediately start stop watch

5. solid sulfur is formed which precipitates in solution, turning cloudy

6. look down at cross and stop the timing when the cross can no longer be seen

7. repeat using different concentrations of sodium thiosulfate solution

required practical: investigating effect of concentration on rate of reaction (measuring gas volume) objective

to investigate the effect of changing concentration on the rate of reaction by measuring the volume of gas given off

required practical: investigating effect of concentration on rate of reaction (measuring gas volume) hypothesis

the same amount of gas will be produced in less time if the concentration of reactants is increased

required practical: investigating effect of concentration on rate of reaction (measuring gas volume) materials

magnesium ribbon cut into 3cm lengths

sulfuric acid 1mol/dm and 1.5mol/dm

conical flask

saftey goggles

gas syringe

stop clock

required practical: investigating effect of concentration on rate of reaction (measuring gas volume) method

1. measure 50cm of 1.0mol/dm H₂SO₄ solution into a flask

2. add the magnesium ribbon to the flask and connect it to the gas collection equipment

3. start stopwatch and record the volume every 10seconds

4. when the reaction is complete repeat using 1.5mol/dm sulfuric acid

required practical: investigating effect of concentration on rate of reaction conclusion

as there are more reactant particles in a given colume collisions occur more frequently, increasing the rate of reaction

what is the collision theory

states that chemical reactions occur only when the reactant particles collide with sufficient energy to react

activation energy

the minimum amount of energy needed in a reaction

a successful collision

means that the reactant particles colliding have sufficient energy

the reactant particles rearrange to form the products

unsuccessful collision

the reactant particles have insufficient energy

the reactant particles just bounce off each other and remain unchanged

rate of reaction affects dependent on the no. successful collisions

the number of particles per unit volume

the frequency of collisions

kinetic energy of the particles

the activation energy

the effect of increasing concentration

a higher conc in particles means that there are more particles present in the same volume so the number of collisions between particles increases causing an increased rate of reaction

the effect of increasing pressure

the higher pressure means that there are the same amount of particles present in a smaller volume so the number of collisions and successful collisions between particles increases causing an increased rate of reaction

the effect of increasing the temp

an increase in temp causes an increase in kinetic energy of the particles - the number of successful collisions increases.

the effect the surface area effects the rate

an increase in surface area means more collisions per second

catalyst

sre substances which speed up the rate of reaction without being altered or consumed

how do catalysts work

they provide an alternate pathway for the reaction to occur, the pathway requires lower activation energy

whats a biological catalyst

enzyme