Rate of reaction Flashcards
Rate of reaction equation
rate or reaction=amount of reactant used OR product formed/time taken
Measuring the amount of reactant used
Units for rate of reaction is g/s or mol
concentration of the reactant=amount (mol)/volume of the reaction mixture (dm3) UNITS ARE MOL/DM3
As the reaction takes place the reactant is being used up
so the reactant decreases
If the product is gas measure the mass in grams
Amount of product formed
Amount of product is formed=total volume of gas produced(cm3)/time taken for the reaction to happen
UNITS ARE CM3/S
Measuring the time it takes for a reaction mixture to become opaque or change colour
Rate of reaction=1/time taken for solution to change colour
Collison theory
Chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy. Minimum amount of energy required to cause a reaction is called activation energy
There are four factors that affect the rate of reaction
TEMPRETURE
CONCENTRATION
CATALYST
SURFACE AREA
Concentration
high conc, increases the number of particles in the same volume
Increasing pressure of reacting gases increases frequency of collisions and same number of particles are now in a smaller space
If the conc is increased it will decrease the amount
if it decreases it will increase the amount
Temperature
In a hot reaction the particles move more quickly, they collide more often with greater energy so more successful collisions.
Surface Area
When a solid is grinded it has a larger surface area
More particles are exposed and available for collisions so there are more collisions and a faster reaction
The particles in a solution can only react with particles on the surface of the area
Catalyst
Reduces amount of energy needed for a successful collision
speeds up a reaction
provides a surface area for the molecules to attach which increases their chances of bumping in to each other
Speeds up both the forward and reverse reaction
reversible reaction
product can react to produce the original reactant
exothermic in one direction and endothermic in the opposite direction
Same amount of energy is transferred
closed systems
No reactant are added and no products are removed
When a reversible reaction occurs in a closed system an equilibrium is achieved when the rate of the forward reaction is equal to the rate of the backward reaction.
Le chateliers’s principle
EXOTHERMIC REACTION
Decreasing temp will shift equilibrium in the exothermic direction
EXOTHERMIC REACTION
temp raised ,yield decrease’s
temp lowers, yield increase’s
Le chateliers’s Principle
ENDOTHERMIC REACTION
Increasing temperature will shift equilibrium in the endothermic direction
ENDOTHERMIC REACTION
Temp raised, Yield increases
Temp lowers, yield decreases
Le chateliers’s Principle
PRESSURE
PRESSURE
Increase pressure causes the equilibrium positions to shift to the side with fewer molecules of gas. Yield decrease
Decrease pressure causes the equilibrium position to shift to the side with more molecules of gas. yield increases
Highest-lowest moles
Le chateliers’s Principle
REACTANTS
Remove reactants-move to rate reactant
Add reactant-move to make product
Le chateliers principle
A reaction in equilibrium will move in the direction to oppose change.
Graphs
steeper the line faster the reaction
When one of the reactant is used up the reaction stops
Investigate how changes in concentration affect the rates of reactions by monitoring a change in colour or
turbidity
40 g/dm3 sodium thiosulfate solution • 1.0 mol/dm3 dilute hydrochloric acid • a conical flask (100 cm3) • a printed black paper cross • a stop clock.
1) Use a measuring cylinder to put 10cm3 of sodium thiosulfate solution into a conical flask and place it on a printed black cross
2) Then add 10cm3 of hydrochloric acid into the conical flask
3) Swirl the solution and start the stopwatch and look down through the top of the flask after a certain time the solution will turn cloudy and stop the clock when you can no longer see the cross
4) Carry out the experiment again using a lower conc of sodium thiosulfate solution
5) Repeat the whole experiment and cal mean value for each conc of sodium thiosulfate
PROBLEM
Because everyone has different eyesight some may be able to see the cross for longer but if you all have the same printed cross it should be fine
IV-conc of the acid
DV-How long it takes for the cross to disappear
CV-volume of acid and conc and volume of sodium thiosulfate
Investigate how changes in concentration affect the rates of reactions by both
measuring the volume of a gas produced
magnesium ribbon cut into 3 cm lengths • dilute hydrochloric acid, 1.0 mol/dm3 and 1.5 mol/dm3 • safety goggles • conical flask (100 cm3) • single-holed rubber bung and delivery tube to fit conical flask • water trough • two measuring cylinders (100 cm3) • clamp stand, boss and clamp • stop clock.
1) Use a measuring cylinder to place 50cm3 of hydrochloric acid into a conical flask
2) Attach the conical flask to a bung and delivery tube
3) Place the delivery tube into a container filled with water
4) Place an upturned measuring cylinder also filled with water over the delivery tube
5) Then add a 3cm strip of Mg to hydrochloric acid and start the stop watch
6) Every 10 seconds measure the volume of hydrogen gas in the measuring cylinder continue until no more hydrogen is given off
7) Repeat the experiment using diff conc of hydrochloric acid
IV-
DV-amount of hydrogen being produced
CV-Amount of hydrochloric acid
