The rate and extent of chemical change Flashcards
What are the 2 formulas to find the rate of reaction?
momr = quantity of products formed / time taken
momr = quantity of reactants used up / time taken
What can the quantity of reactant or product be measured by?
The quantity of reactant or product can be measured by the mass in grams or by a volume in cm3 .
How does the slop of the line give us an idea of the rate of reaction?
-The steeper the slop the faster the reaction
Why would the reaction be fast at the start?
We are making a lot of product at a short span of time because we have a large number of reacting molecules
How do we find the mean rate of reaction at a specific point by a tangent?
Change in “y” / Change in “x”
What does it mean if the slope of the line becomes less steep?
The reaction is slowing down because a lot of the reactant molecules have already reacted and turned into product.
Meaning there are few reactant molecules available to react with.
What is the collision theory?
chemical reactions can occur only when reacting particles collide with each other and with sufficient energy.
How is the rate of a chemical reaction determined by?
By the frequency of successful collisions.
The word frequency means the number of successful collisions per second
What happens when increasing the concentration of reactants in solution?
-Higher concentration → More particles in the same space → More collisions → Faster reaction.
-Higher pressure (for gases) → Particles are closer together → More collisions → Faster reaction.
-Greater surface area (for solids) → More exposed particles → More collisions → Faster reaction.
What happens when you increase the temperature of a chemical reaction?
Increasing the temperature increases the frequency of collisions and makes the collisions more energetic, and so increases the rate of reaction.
What is the chemical reaction in Required Practical 5: Rates of Reaction Disappearing Cross Experiment?
Sodium thiosulfate + hydrochloric acid —-D sulfur (solid)
What does the sulfur make the solution go in Required Practical 5: Rates of Reaction Disappearing Cross Experiment?
Causes TURBIDITY (cloudy)
What is the process of Required Practical 5: Rates of Reaction Disappearing Cross Experiment?
- Use a measuring cylinder to put 10cm3 of sodium thiosulfate solution into a conical flask
- Place the conical flask onto a printed black cross
- We then add 10cm3 of hydrochloric acid into the conical flask
- Swirl the solution and start the stop watch
- Look down the flask and once the solution goes cloudy and prevents us from seeing the black cross no more we stop the stop watch
- We carry out the experimentation again using now lower concentrations of sodium thiosulfate
- Repeat the whole experiment and find the mean values of the conc. of the sodium thiosulfate solution
What are we investigating in Required Practical 5: Rates of Reaction?
how changes in concentration affect the rates of reactions
What does it mean if it’s reproducible?
If it can be carried out by another person or different technique or equipment and still get the same results.
What is the problem with Disappearing Cross Experiment?
Different people have different eyesight’s
What is the chemical reaction in Required Practical 5: Rates of Reaction Gas Collection Experiment?
Magnesium + hydrochloric acid = magnesium chloride + hydrogen gas
What is the process of Required Practical 5: Rates of Reaction COLLECTING GAS Experiment?
- Using a measuring cylinder we place 50cm3 of hydrochloric acid into a conical flask.
- We then attach the conical flask to a bung with a delivery tube
- We place the delivery tube into a container filled with water
- Then place an upturned measuring cylinder also filled with water over a delivery tube
- We then add 3cm strip of magnesium to hydrochloric acid in the conical flask and start the stopwatch
- The reaction produces hydrogen gas which is trapped in the measuring cylinder
- Every 10 secs. we count the vol. of hydrogen gas in the measuring cylinder continuing until no more hydrogen is given off
- Repeat the experiment using different amount of hydrochloric acid
What does Required Practical 5: Rates of Reaction show us?
The greater the conc. of a chemical in a reaction the faster the reaction take place.
What can particles in a solution only react with?
Particles in a solution can only react with particles on the surface of the solid.
What happens when we increase the surface area?
More collision per sec.
Meaning the rate of reaction increases.
Why would smaller block increase the rate of reaction?
Surface area : volume
What would happen if you increase the temperature of the chemical reaction?
Increases the rate of reaction.
Because increasing the temperature increases the energy of the particles.
Now because the particles have more energy they now move faster.
Increasing the frequency of collisions.
What does this mean if each collision has more energy?
Can overcome the activation energy and collide successfully
What are catalysts?
Catalysts increase the rate of chemical reactions but are not used up during the reaction.
Why are catalysts helpful?
They allow us to carry out reaction without needing to increase the temperature. This saves money.
Because they are not used up during the reaction, we can reuse them again and again.
How do catalysts increase the rate of reaction?
by providing a different pathway for the reaction that has a lower activation energy.
Meaning more particles can collide with each other increasing the rate of reaction.
What are key points of catalysts?
-We do not include them in the chemical equations
-Different reactions need different catalysts
-Enzymes act as catalysts in living organisms
How can we change the direction of the reversible reaction?
By changing the conditions.
What are the 2 main points for energy in reversible reactions?
-If the reaction is endothermic in one direction, its exothermic the other direction (hydrated copper sulfate)
-The same amount of energy is transferred in each case
What is equilibrium?
When the forward and reverse reactions occur at the same rate
What will happen if their is change in a equilibrium system?
If a system is at equilibrium and a change is made to any of the
conditions, then the system responds to counteract the change.
This is called Le Chatelier’s Principle.
What is Le Chatelier’s Principle?
Le Chatelier’s Principle is if a system is at equilibrium and a change is made to any of the
conditions, then the system responds to counteract the change.
What would happen if there was an increase in pressure for gaseous reactions at equilibrium?
an increase in pressure causes the equilibrium position to
shift towards the side with the smaller number of molecules
What would happen if there was an decrease in pressure for gaseous reactions at equilibrium?
a decrease in pressure causes the equilibrium position to shift
towards the side with the larger number of molecule
What would happen if there was an increase in temperature of a equilibrium reaction?
If we increase the temperature of this system then the equilibrium shift to the endothermic side to reduce temperature.
Because energy is taken in causing temp. to fall.
What would happen if there was an decrease in temperature of a equilibrium reaction?
