1.9 Rates of Reaction
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What is the rate of reaction measured in?
The increase of [products] or the decrease in [reactants]
What is the rate equation?
Rate= k[A]^m[B]^n
What do orders mean?
Order=0 if changing conc doesn’t change rate Order=1 if doubling conc doubles the rate Order=2 if doubling conc quadruples rate
What is the rate determining step?
The step in a mechanism that determines what order a reaction is which are then involved in the rate equation
What is the definition of an order?
The number of molecues of each species in the rate dependent step
What are the units of rate if the total order is 0?
Moldm^-3s-1
What are the units if the total order is 1?
S^-1
How do you find the order from a data table?
• Pick two rows where one of the concentrations remain constant 2.Calculate the change by dividing one by the other of the concentrations of substance you want the order if 3.Calculate the change in rate • If rate doesn’t change - Order 0 If rate changes the same as the concentration- Order 1 If rate changes double the amount of the concentration- Order 2
What is the iodine clock measuring?
The rate for iodide ions to become iodine
How is the iodine clock experiment able to be measured?
Iodine produced will react with sodium thiosulfate until thiosulfate runs out forming Iodide ions again
Why are initial rates used in rate calculations?
The concentrations are known
How is the initial rate obtained from a graph?
Tangent at the start of the curve
What happens to the rate equation if a large concentration of one reactant is added in comparison to the others?
Concentration will be high enough that it is a constant
What is the opposite of exponential in the Arrhenius equation?
Natural log
What are the only things which affect the rate constant?
Temperature Catalysts
What is the Arrhenius constant in reference to?
• The frequency of collisions • Varies only slightly with temperature so taken as a constant
What are the units of activation energy in the Arrhenius equation?
J/mol
What denotes the order in the rate determining step?
The number of particles involved
Why does increasing the temperature make a reaction go faster?
Particles have more kinetic energy so more frequent collisions More particles with a greater frequency of successful collisions
What does a catalyst do and how does it do it?
• Speeds up the rate of reaction • Providing a lower activation energy through an alternative reaction route
Why in terms of particles does adding a catalyst make the reaction go faster?
• E >/= Ea • More particles with a greater frequency of successful collisions • Increases rate of reaction
How can the rate equation be calculated from the overall equation?
• Not possible
What is the definition of a mechanism?
• The breakdown of steps in a reaction
How can a chemical be put into a rate equation but not the overall equation?
Catalysts as they are part of the rate determining step but not the overall equation