Chapter 18 Flashcards
Definition of rate of reaction
The change in concentration of a reactant or product in a given time
Rate is equal to:
Quantity reacted or produced/ time
Or
Change in concentration/ time
What are the units of rate?
Moldm-3s-1
What does |A| mean
Shorthand for the concentration of a in moldm-3
What is rate of reaction proportional to?
A reactant to a given power
Rate (fish sign) |A|^n
What is an order?
The power to which the concentration of a reactant is raised in the rate equation
What does zero order mean
Concentration does not influence rate
What does first order mean
The rate depends on concentration raised to the power of 1
What does second-order mean
The rate depends on the concentration raised to the power of 2
What is the rate equation
Rate= k|A|^m |B|^n
What is the rate constant
the rate constant is the constant that links rate of reaction to concentration of reactants related to the powers of their orders in the rate equation
What is overall order
Overall order is the sum of the individual orders of reactants in the rate equation
How do you determine the units of the rate constant
1) Rearrange to make k the subject
2) Substitute the units of rate and the concentrations
3) simplify
How can you find the rate constant from experimental results
By looking at the relationship between the change in concentration and the change in rate eg concentration doubles, rate quadruples means second order
What does zero-order look like on a concentration time graph
A straight line with a negative gradient
What does first order look like on a concentration time graph
A downward curve with a decreasing gradient
What is half life
The time taken for the concentration of a reactant to have which is constant in a first-order concentration
What is a gradient of a concentration time graph equal to
The gradient of a concentration time graph is equal to the rate
How do you measure Half-Life from a concentration time graph
Draw a line at half concentration until it meets the graph then down to the time repeat at a quarter and an eighth and then take an average
How do you determine k from the rate and a concentration time graph
1) Rearrange to make k the subject
2) Find the rate by the gradient
3) divide by the initial concentration
How do you determine k from the half-life
K= ln2/ T1/2
How can you investigate reaction rates using the initial rates method
1) Add starch to an excess of hydrogen peroxide
2) Add a small amount of sodium thiosulfate
3) the sodium thiosulfate will react with the iodine and will be used up when all the sodium thiosulfate is gone the mixture will turn blue black
4) time how long it takes to change colour
5) vary concentration
How can you investigate reaction rate using the continuous monitoring method
Calibrate the colorimeter with water
Measure the absorbance of the solution before the reaction begins
Start the reaction and take readings at regular intervals
use a calibration curve to convert absorbance to concentration
Plot on a concentration time graph
What is the rate determining step
The slowest step in a multi step reaction
Why can you predict reaction mechanisms using the rate determining step
The rate equation only includes reacting species involved in the rate-determining step
The orders in the rate equation match the numbers of species in the rate determining step
What needs to happen for a reaction to take place
Particles need to collide the sufficient energy and correct orientation
What effect does increasing temperature have on the rate of a reaction and the rate constant
increasing temperature increases speed which increases the frequency of collisions and also energy so a greater proportion have sufficient energy therefore the rate increases and changes the rate constant
What is the arhenius equation
An exponential relationship between rate constant and temperature
K= Ae^-Ea/RT
What is the arhenius equation in logarithmic form and its relationship to y=Mx + c
ln k =( -Ea/R)(1/t) + lnA
Y= Mx +c
How can you find the activation energy and pre exponential factor using the a graph of lnk against 1/t
The gradient is equal to -Ea/R so find the gradient and multiply it by the rate constant r to find the activation energy
Find the y intercept which is equal to lnA and put it as a power of e
