x Turn on thread page Beta
 You are Here: Home

# Expressing rates of change watch

1. Hi people, just looking for some quick guidance as my exam's on Wednesday. My textbook has a straight line graph of [Reactant] (x) against Time (t). A gradient triangle is drawn underneath a line segment from two points A to B. What I'm struggling is the text underneath which says:

"The slope of AB is exactly equal to the slope of the graph, since the graph is a straight line between A and B (fine). This graph represents a constant reaction rate - at any point between A and B, the instantaneous rate and the average rate between A and B are the same, Δ = x/Δt." (not fine) Whilst I know the difference between initial, instantaneous and average rate, I don't know what their equation means... btw the gradient triangle is labelled Δx and Δt, as expected.

2. (Original post by Va Sin Decir)
Hi people, just looking for some quick guidance as my exam's on Wednesday. My textbook has a straight line graph of [Reactant] (x) against Time (t). A gradient triangle is drawn underneath a line segment from two points A to B. What I'm struggling is the text underneath which says:

"The slope of AB is exactly equal to the slope of the graph, since the graph is a straight line between A and B (fine). This graph represents a constant reaction rate - at any point between A and B, the instantaneous rate and the average rate between A and B are the same, Δ = x/Δt." (not fine) Whilst I know the difference between initial, instantaneous and average rate, I don't know what their equation means... btw the gradient triangle is labelled Δx and Δt, as expected.

x in this case is concentration

As rate of reaction is defined as the change of concentration over time, hence the gradient = rate of reaction = change in x / change in time

This is only true for a system where only one concentration of your reactants are changing, ie the rest are fixed. This is a technique commonly used in kinetics to determine order of reaction with respect to this specific reactant.
3. (Original post by shengoc)
x in this case is concentration

As rate of reaction is defined as the change of concentration over time, hence the gradient = rate of reaction = change in x / change in time

This is only true for a system where only one concentration of your reactants are changing, ie the rest are fixed. This is a technique commonly used in kinetics to determine order of reaction with respect to this specific reactant.
Thanks, but "Δ = x/Δt" still doesn't make sense - I know that rate = Δx/Δt but that's not what my book says.
4. (Original post by Va Sin Decir)
Thanks, but "Δ = x/Δt" still doesn't make sense - I know that rate = Δx/Δt but that's not what my book says.
Hmm, delta stands for a change, so I can't see why the book is stating it that way, I would probably think of it as

change(gradient) = change in x / change in t

I don't really know, perhaps check with your teacher, there tends to be one or two minor mistakes for most textbooks.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: January 24, 2010
Today on TSR

### Unconditional offer...

But going to get a U!

### Can I date a girl with no boobs?

Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE