The Effect Of Concentration On The Rate Of A Reaction

Submitted By haj95
Words: 1351
Pages: 6
Open Document
Practical Work for Learning

The effect of concentration on the rate of a reaction © Nuffield Foundation 2013

Chemical reactions can be ... fast… © Nuffield Foundation 2013

…or slow.

Learning outcomes
You will be able to ...
• evaluate different models for explaining the rates of reactions • use experimental data to identify how the concentration of each reactant affects the rate of a reaction © Nuffield Foundation 2013

What you already know
Organise what you know about the reaction of marble chips with hydrochloric acid into three categories.
Practical techniques equipment and methods
Observations / data / summaries of data including from previous experimental work, e.g. graphs, or statements summarising a trend/pattern
Explanations
inferences, models, type of reaction, equations

© Nuffield Foundation 2013

What is rate of reaction?
In a chemical reaction, reactants are used up and products form.
A + B  products
In this reaction A and B are the reactants. They are used up.
Rate of reaction is the rate at which reactants are converted to products. © Nuffield Foundation 2013

Models of rate
Collision theory can make qualitative predictions.
It can predict how the rate may change with changing conditions – but not by how much.
A mathematical model can make quantitative predictions.
A rate equation is a mathematical model.
(This is different from the chemical equation for the reaction).
What is the relationship between rate and the concentration of acid in the reaction with marble chips?
© Nuffield Foundation 2013

A mathematical model
The rate could be proportional to the concentration of acid: rHCl ∝[HCl] or rHCl = k[HCl] rHCl = rate of change of concentration of HCl
(mol dm–3 s –1) k = a constant (the rate constant)
[HCl] = concentration of HCl (mol dm-3)
If this was the mathematical relationship between rate and concentration, what would the graph look like?

© Nuffield Foundation 2013

A mathematical model rHCl = k[HCl]
If the rate is proportional to the concentration of acid…
…the graph will look like this.
Double the concentration, and the rate doubles.

© Nuffield Foundation 2013

A mathematical model
The rate could be proportional to the square of the concentration of acid:

rHCl ∝[HCl]2 or rHCl = k[HCl]2
If this was the mathematical relationship between rate and concentration, what would the graph look like?
© Nuffield Foundation 2013

A mathematical model rHCl = k[HCl]2
If the rate is proportional to the square of the concentration of acid…
…the graph will look like this.
Double the concentration, and the rate goes up 4 times (22).
© Nuffield Foundation 2013

A mathematical model
Maybe the rate is constant and is not affected the concentration of acid at all:

rHCl = k or rHCl = k[HCl]0
If this was the mathematical relationship between rate and concentration, what would the graph look like?

© Nuffield Foundation 2013

A mathematical model rHCl = k

If the rate is not affected by the concentration of acid…
…the graph will look like this.
Double the concentration, and the rate stays exactly the same.
© Nuffield Foundation 2013

Rate and concentration
So there are three possible models: rHCl = k

This is called zero order ([HCl]0)

rHCl = k[HCl]

This is called first order ([HCl]1)

rHCl = k[HCl]2

This is called second order ([HCl]2)

To find the order of reaction for marble and acid we need to collect some data …
© Nuffield Foundation 2013

Rate and concentration
So, how can you measure rate?
Rate cannot be measured directly. So what can we measure?
• Time
• Concentration
• Volume of gas
• Change in mass
© Nuffield Foundation 2013

Rate and concentration
Rate of change of concentration cannot be measured directly.
It can be found by analysing measurements of concentration over time. How fast is the concentration falling at any one time? The gradient of the concentration–time graph tells us about the rate.
A steep gradient means a fast rate.
A shallow gradient means a slow rate.
© Nuffield
Show More

Related Documents: The Effect Of Concentration On The Rate Of A Reaction

Microbio notes Essay

Sterile techniques in surgical settings (military) John Snow Infection control & epidemiology Cholera outbreak in London Joseph Lister Antiseptic techniques Listerine Ignaz Semmelweiz Handwashing Perpetual Fever caused deaths of mothers Death rates increased in ward w/ med students (using cadavers & not washing hands in b/t patients) Germ Theory of Disease Formulated by Pasteur, proved by Koch *The theory that many disease are caused by the presence and actions of microorganisms in the body…

Words 6946 - Pages 28

BIOL319 Exam 3 Complete Review Essay

*It’s that time again! I’ll add each review as he posts them. Don’t adjust colors, etc.--except for answers in one diff color unless you have saved it on your own desktop, thanks! ***make sure not to try and copy this document because it could delete the entire thing, if you want to save it go to file and then download it**** JUST ADDED THE 3RD REVIEW*** Study guide for lecture that was cancelled: Page 253 -Be able to recognize the definition of a bursa or a tendon sheath. Be able to recognize…

Words 7729 - Pages 31