Paper 2 C6 - The Rate and Extent of Chemical Change Flashcards
Give the two equations used to calculate rate of reaction
reactants used/time
products formed/time
Give the two possible units for rate of reaction
cm³/s
mol/s
Give one observation that can be made on a graph when a reaction finishes
The graph levels off
Describe how to calculate the rate of reaction at a specific point on a graph
- Draw a tangent to the curve
- Calculate the gradient of the tangent
The steeper the tangent of a rate of reacton graph, the _________ the reaction
faster
Identify five factors that affect the rate of chemical reactions
- Concentration
- Pressure
- Surface area
- Temperature
- Catalysts
Define collision theory
Theory that a chemical reaction only happens if particles collide with enough energy
Define activation energy
Minimum amount of energy particles need to react
Explain why an increase in temperature increases rate of reaction
Increases kinetic energy of particles
–> More frequent, energetic collisions
—> Faster rate of reaction
Explain why an increase in surface area increases rate of reaction
More area for reactant particles to collide with
–> More frequent successful collisions
—> Faster rate of reaction
Explain why an increase in concentration of a solution increases rate of reaction
Particles are closer together
–> More frequent successful collisions
—> Faster rate of reaction
Explain why an increase in pressure increases rate of reaction
Particles are closer together
–> More frequent successful collisions
—> Faster rate of reaction
Define catalyst
Substance that speeds up a chemical reaction without being used up
Explain how catalysts increase the rate of a reaction
Provide alternative pathway with lower activation energy
–> More particles have enough energy to react
—> More frequent successful collisions
True/False: Catalysts increase the overall energy change of a reaction
False - it stays the same
Plan an experiment to investigate how the concentration of a reactant affects the rate of reaction (disappearing cross experiment)
- Use a measuring cylinder to put 10 cm³ of sodium thiosulfate into a conical flask
- Place the conical flask onto a printed black cross
- Add 10cm³ of hydrochloric acid to the conical flask
- Swirl solution and start a stopwatch
- Look down through the top of the flask
- Stop the clock when the cross can no longer be seen
- Repeat experiment using different concentrations of sodium thiosulfate
Give two control variables in the disappearing cross experiment
- Volume of sodium thiosulfate
- Volume and concentration of hydrochloric acid
Give one independent variable in the disappearing cross experiment
Concentration of sodium thiosulfate
Give one dependent variable in the disappearing cross experiment
Time taken for cross to disappear
Suggest one problem with the diappearing cross experiment
People have different eyesights, so may not get the same results
Plan an experiment to investigate how the concentration of a reactant affects the rate of reaction (volume of gas released)
- Use a measuring cylinder to put 50cm³ of hydrochloric acid into a conical flask
- Connect the bung and delivery tube to the flask
- Connect the tube to the gas syringe/upside down measuring cylinder
- Add a 3cm piece of magnesium ribbon to the flask
- Start a stopwatch
- Record the volume of hydrogen gas collected every 10 seconds
- Continue until no more hydrogen is given off
- Repeat experiment with different concentrations of hydrochloric acid
Give one independent variable in the rate of reaction (volume of hydrogen released) experiment
Concentration of hydrochloric acid
Give one dependent variable in the rate of reaction (volume of hydrogen released) experiment
Time taken for hydrogen to stop being produced
Give one control variable in the rate of reaction (volume of hydrogen released) experiment
Length/mass of magnesium ribbon
Name the type of reaction that includes the products reacting to form the original reactants
Reversible reaction
Write the symbol used to represent a reversible reaction
⇌
Give an example of a reversible reaction
The Haber process
nitrogen + hydrogen ⇌ ammonia
N₂ + 3H₂ ⇌ 2NH₃
If a reversible reaction is endothermic in one direction, it will be ___________ in the ______ direction
exothermic, other
In a reversible reaction, the same amount of ______ is transferred each way
energy
Give a synonym for a closed system
A sealed container
Define equilibrium
When the rate of a forward reaction is equal to the rate of a backward reaction
Name the system that equilibrium can take place in
Closed system
State why equilibrium can be reached in a closed system
Products/reactants cannot escape
Name the principle that predicts how an equilibrium responds to changes in different conditions
Le Chatelier’s Principle
State why equilibriums respond to changes in conditions
To keep the amount of reactant relative to the amount of product stable
Describe how increased concentration of reactants affect the position of equilibrium
Forward reaction is favoured
–> Equilibrium shifts towards products
—> More product is made
Describe how increased concentration of products affect the position of equilibrium
Backward reaction is favoured
–> Equilibrium shifts towards reactants
—> More reactant is made
Describe how increased temperature affects the position of equilibrium
Equilibrium shifts in direction of endothermic reaction
–> (decreases temperature back to normal)
Describe how decreased temperature affects the position of equilibrium
Equilibrium shifts in direction of exothermic reaction
–> (increases temperature back to normal)
Describe how increased pressure affects the position of equilibrium
Equilibrium shifts to side with fewer molecules
–> (increased rate of reaction creates more)
Describe how decreased pressure affects the position of equilibrium
Equilibrium shifts to side with more molecules
–> (decreased rate of reaction creates less)
True/False: Changing the pressure has no effect on a reversible reaction unless one of the products or reactants is a gas.
True
