• Find a friend, and each of you crumple up a piece of paper. Sitting facing one another, with knees almost touching, toss your pieces of paper together, trying to get them to hit while still in the air. Do this 10 times - how many successful "collisions" did you record? • Now, grab another friend with their own wad of paper. This time, a successful collision will only occur when all three pieces of paper hit together simultaneously - just two out of three won't do. Out of 10 tosses, how many are successful? Add one more friend and repeat the exercise. Any successful collisions, where all four pieces of paper collide at the same instant?
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Transcript
• Find a friend, and each of you crumple up a piece of paper. Sitting facing one another, with knees almost touching, toss your pieces of paper together, trying to get them to hit while still in the air. Do this 10 times - how many successful "collisions" did you record?
• Now, grab another friend with their own wad of paper. This time, a successful collision will only occur when all three pieces of paper hit together simultaneously - just two out of three won't do. Out of 10 tosses, how many are successful?
Add one more friend and repeat the exercise. Any successful collisions, where all four pieces of paper collide at the same instant?
HL Kinetics
Syllabus
16.1 Rate Expression
• Understand– Rate constant– Overall order– Order of reaction
• Use experimental data to deduce rate expression.
• Solve problems using the rate expression.
KINETICS GIVES US CLUES TO A REACTION MECHANISMTHIS IS ALL EXPERIMENTALLY DETERMINED
DEFINITIONS
• Rate is how fast concentration of reactant is falling ( or vice versa ) measured in – mol dm-3 s -1
• Rate Constant (k) is only constant if T and Ea stays constant. A catalyst or higher T would increase k. Changes in concentration do not.
The Concentration Terms
• Where rate = k[A]a [B]b [C]c
• The powers are called the ‘order of reaction’.– If no effect on rate regardless of concentration we call it zero order.– If we double concentration of [A], and the rate doubles we say Rate
= k[A]– If we double concentration of [A], and rate is quadrupled we say
Rate = k[A]1
– If we double the concentration of [A}, and the rate is 8x faster we say Rate = k [A]2
• Overall orders are sums of the individual orders.
Orders of Reaction
• xA + yB + zC…… products
• Rate = k [A]x [B]y [C]z this is rate equation
• How do we measure rate of reaction ?
– How fast concentration of one of reactants is falling
– Units
Zero Order
• This means the concentration of that substance does not influence the rate
• Rate = k[A]0
First Order
• Whatever you do to the concentration, you do to the rate.