Rates Of Reaction Flashcards
Collision theory
States that in order for a reaction to occur, particles must collide with each other with enough energy to react.
Activation energy
The minimum amount of energy required for a successful collision to occur
The rate of reaction is dependent on…
Surface area, volume, catalysts, conc/pressure
How does SA affect rate of reaction?
- increasing SA = faster rate
- smaller objects have larger SA
- more particles are exposed to the surface of the solid
- more frequent collisions between particles = faster rate
How does concentration of solid + pressure of gas affect rate of reaction?
- higher conc. of solid / higher pressure of gas = faster rate
- this is because there are more particles in the same volume
- increases frequency of collisions
- therefore increases number of successful collisions = faster rate of reaction
How does temperature affect rate of reaction?
- higher temp. = faster rate
- high temp. = more kinetic energy
- makes particles move around faster
- higher frequency of collisions = more successful ones = faster rate
What is the other reason about how temperature affects rate?
At higher temperatures, more particles will have energy greater than or equal to the activation energy, meaning more successful collisions will occur = faster rate
Catalyst
A chemical substance that increases the rate of reaction by providing an alternate reaction pathway with a lower activation energy. It remains chemically unchanged at the end of the reaction.
Describe the SA experiment
- marble chips of large + small size but the same mass are put into a conical flask each of dilute hydrochloric acid
- then time taken for the solution to produce 100cm3 of CO2 is measured for both the large and small marble chips
- the smaller ones took the least amt. of time as they had a larger SA:V ratio
What are marble chips actually made of?
Calcium carbonate (CaCO3)
Describe the concentration experiment
Same setup as the SA version, but the only difference is that the concentration of the hydrochloric acid is changed between 2mol/dm3 to 0.4mol/dm3 in increments of 0.4. The volume of acid remains the same
Describe the temperature experiment
- sodium thiosulfate and hydrochloric acid are put into a flask inside a water bath with a black cross underneath
- then time taken for the solution to go cloudy is measured
- temperature of water bath varied between ice cold, room temp, warm and boiling water to see which made solution turn cloudy the quickest
- the boiling water one turned cloudy the quickest as high temperature increases rate
Word equation for the temperature experiment
Sodium thiosulfate + hydrochloric acid => sodium chloride + sulfur + sulfur dioxide + water
Describe the catalyst experiment
- 4 compounds (copper,copper oxide, manganese oxide and potassium iodide) were placed in hydrogen peroxide to see which one would catalyse its decomposition into water and oxygen
- manganese oxide was the catalyst as it made the solution effervesce vigorously and produce heat and steam
What does hydrogen peroxide naturally decompose into?
Water and oxygen
Balanced equation for decomposition of hydrogen peroxide
2H2O2 => 2H2O + 2O2
What happened when copper oxide was put into the hydrogen peroxide?
Solution turned black (but this was because CuO is black), small bubbles were produced
What happened when manganese oxide was put into the hydrogen peroxide?
Steam was produced, lots of heat and vigorous effervescence
What happened when copper was put into hydrogen peroxide?
No change
What happened when potassium iodide was put into hydrogen peroxide?
Solution turned yellow, effervescence and heat
Rate of reaction formula
Change in amount of product/time or 1/time
Rate of reaction units
Cm3/s
How do you find rate of reaction at a specific moment on the graph?
- read off the x axis to see where that specific moment touches the curve
- then draw a tangent touching that specific part of the curve
- then find the gradient of the tangent using rise/run
Explain why gradient is steep at start of experiment
At the start, there’s a high concentration of reactant particles. This means that:
- more frequent collisions between particles
- faster rate = steeper gradient
Explain why gradient decreases as time goes on in an experiment
Later on, concentration of reactant particles starts decreasing. This means that:
- there are less frequent collisions
- this results in a slower rate which is shown as a shallower gradient on the graph
Explain why gradient is 0 at the end of the experiment
At the end, the reaction has finished and all of the reactant particles are used up. This means that there are no particles for collisions to occur, so rate is 0 so gradient is also 0.
How do catalysts enable companies to reduce costs?
They allow chemical reactions to occur at lower temperatures meaning that less energy is required for the reaction to take place
