Physical Chemistry Flashcards
Rate of chemical reaction depends on :
1) frequency of collisions
2) particles have to collide w/enough energy for collision to be successful
You can work out speed of reaction by recording:
1) amount of product formed
2) amount of reactant used up
* divide by time taken
Activation energy
AE is the minimum energy a particle needs for a successful collision
catalyst
Catalyst is a substance that speeds up a reaction without being used up or changed after reaction
How does using a catalyst effect rate of reaction ?
Catalysts speed up reaction
Because they provide an alternative pathway of lower activation energy meaning less time spent for particles to react= faster reaction
Explain why increasing the temperature increases rate of reaction?(2 reasons)
- increase in temp= more kinetic energy= particles collide more
- the particles have to collide w/ a minimum amount of energy( ACTIVATION ENERGY) and when u increase the temp more particles have energy more than or equal to the AE = more successful collisions
What is bond breaking?
When energy absorbed = endothermic reaction ( 🔺H = +ve)
What is bond making?
When energy released= exothermic reaction (🔺H= -ve)
How does changing the concentration effect rate of reaction
By increasing the concentration of acid, we increase the NUMBER OF ACID PARTICLES in a fixed volume—
particles are closer together + COLLIDE MORE FREQUENTLY= more SUCCESSFUL COLLISIONS
Rate of reaction
How fast reactants are turned into products
What word is used to describe a reaction in which there is a temperature rise
Exothermic
What word is used to describe a reaction where the temperature has dropped
Endothermic
Endothermic
Reactions in which heat energy is taken in from the surroundings 🥶
Exothermic
Reactions in which heat energy is given out to the surroundings 🔥
In exothermic reactions what has more chemical energy: the products or the reactants?
The reactants have more chemical energy
The products have less chemical energy
Chemical energy—> heat energy
(Heat energy released to surroundings)
In endothermic reactions what has more chemical energy: the products or the reactants?
The products have more chemical energy
The reactants have less chemical energy
Heat energy—> chemical energy
What is enthalpy change a measure of ?
The amount of heat energy taken in or given out in a chemical reaction.
Has the symbol: 🔺H
Green Copper(ii)carbonate thermally decomposes to what (give colours change) and what type of reaction is this ?
It’s an endothermic reaction
Upon thermal decomposition it produces copper (ii) oxide which is BLACK
Define the specific heat capacity of a substance
Amount of heat needed to raise the temperature of 1 gram of a substance by 1^C
How does one work out the MOLAR ENTHALPY CHANGE after obtaining (Q= heat energy change)
1) work out number of MOLES of the substance burned/reacted
moles= mass/RAM
2) now work out enthalpy change: by plugging in the Q value (heat energy change)
molar enthalpy change= Q/ number of moles of the substance
Set up a dissolving experiment to measure enthalpy change using calorimetry
~ set up a polystyrene cup insulated with cotton wool containing the reaction mixture and a thermometer
Put water in cup + record temp
Then add anhydrous copper (ii) sulfate
Stir + record temp
Set up a neutralisation experiment to measure enthalpy change using calorimetry
~ set up a polystyrene cup insulated with cotton wool containing the reaction mixture and a thermometer
Put dry citric acid + dry sodium hydrogen carbonate to the cup + record temp
Then separately get some water and measure the temp (of it alone)
Now add the water to the dry mix + record temp
Set up a displacement experiment to measure enthalpy change using calorimetry
~ set up a polystyrene cup insulated with cotton wool containing the reaction mixture and a thermometer
Put copper(ii) sulfate solution in cup + record temp
Then add powdered zinc
Stir + record temp
What is the effect of increasing pressure on rate of reaction of gases
Increasing pressure of gases, increases the rate of reaction because the particles r much closer together, which means they collide more frequently= MORE SUCCESSFUL COLLISIONS
What state does increasing pressure have no effect on and why
Particles in Liquids + solids r very close together and r affected v little by changes in pressure
What happens to the rate of reaction of marble chips in hydrochloric acid if you increase the surface area of the marble chips
The rate of reaction will increase when the SA increases (smaller chip)
Cos there r more surfaces in contact w the acid, So the frequency of successful collisions increases
Do catalysts change by the end of a reaction ?
NO! Catalysts are left unchanged and are not used up in a reaction
Design an experiment to investigate the rate of reaction of calcium carbonate reacting with HCl acid
Put calcium carbonate with HCl acid in a conical flask with a rubber stopper to stop CO2 gas escaping
Attach a gas syringe to the conical flask + measure the CO2 produced
Measure the time taken for the reaction to take place (no more bubbling)
Use amount of product formed
—————————————
Time taken
= rate of reaction
Why are catalysts important in industry
Catalysts r important in industry cos they make substances react quickly at lower temperatures + pressures which would otherwise be necessary
THIS SAVES MONEY 💸💸💸💸💸💸
Is bond breaking an exothermic or endothermic process
Bond breaking = endothermic process
Is bond making an exothermic or endothermic process
Bond making = exothermic process
Set up a calorimetry experiment of COMBUSTION to calculate enthalpy change
1) set up a copper can w water and a thermometer, now underneath the can fill a spirit burner with alcohol
2) record the temperature of the water b4 + weigh the spirit burner and lid
3) light the wick and wait till it reaches 50*C— put out flame
4) weigh spirit burner + lid AGAIN
5) calculate enthalpy change
USE A DRAUGHT EXCLUDER = to prevent unwanted heat loss to surroundings
Energy change =
Energy change = sum of BONDS BROKEN - sum of BONDS MADE
If more energy is released during bond making .. what kind of reaction is it?
More energy is released during bond making so it is an exothermic reaction
-🔺H = exothermic
If more energy is released during bond breaking.. what kind of reaction is it?
More energy is released during bond breaking so it is an endothermic reaction
+🔺H = endothermic
What is the effect of temperature on yield
Increasing the temperature increases the rate of reaction BUT DECREASES THE YIELD
