18.1-18.5 Flashcards
How can rate be measure in experiments
- the change in pH of a reaction
- the amount of mass lost
- volume of gas produced
- colorimeter
How do you measure the rate of reaction if there is a pH change
- could be change in H+ ions used up or produced over time
- use a pH meter to measure the pH of a reaction at regular intervals
How do you measure the rate of reaction if there is an amount of mass lost
- USE FOR PRODUCTS THAT PRODUCE A GAS
- place reaction on balance and measure the mass lost as gas is lost
- use mole calculations to work out number of moles of gas lost
How do you measure the rate of reaction if there is a volume of gas produced
- measure the amount of gas produced using a gas syringe over a specific time
- use ideal gas equation to work out the number of moles of gas produced
How does measuring the rate of reaction using a colorimeter work
- colorimeter measures absorbable of light by a coloured sample
- the more concentrates a sample is the darker its colour and so the more light absorbed
What is a calibration curve
- a graph making up a range of known different concentrations
How do you find a rate from a graph
- from the gradient
= change in y
_______________
Change in x
How do you find the rate on a curved line
1) draw a tangent that meets the curve at a specific point
2) extend the line right across the graph
3)work out the gradient
What is the initial rate
- the rate right at the start of the reaction
How do you work out the initial rate from a curved line
- work out the gradient of the tangent at 0 minutes
What do clock reaction tell us
- how long it takes for a reaction to occur
What do clock reaction simplify
- simplify the initial rate method
What is the disappearing cross experiment
- an experiment monitored where a black cross is underneath the reaction vessel and over time the cross will disappear and you can no longer see it through the beaker.
- there is a colour change= end point
Complete the sentence:
The quicker the clock reaction…
- the faster the initial rate of reaction is
What 3 assumptions do we make for clock reactions
1) the temperature of the reaction remains constant
2) concentration of reactants doesn’t change significantly during the time period of reaction
3) reaction has not proceeded too far when the end point is seen
Based on our assumptions for rate of reaction what can we infer
- that rate of reaction REMAINS constant during the time period you are measuring
- the rate of the clock reaction is a good estimate of the initial rate of reaction
Describe the iodine clock experiment
1) add sodium thiosulfate and starch( which acts as an indicator) to excess hydrogen peroxide
2) sodium thiosulfate reacts immediately with the I2, that is produced in this reaction
3) when there is no more sodium thiosulfate left then the I2 reacts with starch to give a deep blue/black colour
What does varying the concentration of iodine and/or hydrogen peroxide while keeping everything else constant do to the experiment
- results in the time take for the blue/black colour to appear to change
What does the rate equation link together
- rate with concentration
What is the rate equation
Rate= k [A]^a [B]^b
Rate= moldm^3s^-1
K= rate constant (units vary)
A/B= concentration of substances
a/b= orders of the reaction
What do orders of reactions tell us
- how the concentration of the substance affects the rate
What effect does a zero order have on rate
- change in concentration has NO EFFECT on the rate
E.g if [A] doubles the rate doesn’t change
What does a 1st order mean
- changes in concetration has a proportional change on rate
E.g if [A] doubles then the rate doubles
What does 2nd order mean
- changes in concentration has a squared proportional change on the rate of
E.g if [A} doubles then rate quadruples
