## Initial rates

Irma Ramos 2I
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

### Initial rates

Why is it that when comparing different reaction rates, the reaction rate only depends on the reactants? Why do we just compare the initial rates rather than the rates at the end of the reaction as well?

Angel Gomez 1K
Posts: 36
Joined: Fri Sep 29, 2017 7:04 am

### Re: Initial rates

To explain why we compare initial rates, we can refer to the following equation that Lavelle used in class:
$NH_{4}^{+}(aq)+NO_{2}^{-}(aq)\rightarrow N_{2}(g)+H_{2}O(l))$
Since N2 is a gas, it leaves the solution. As a result the reverse reaction is less likely to occur because there is a lower amount of N2(g) to produce reactants.
It's easier to observe initial rates, so that is why we learned the method of initial rates to determine k and n.

Tatiana Hage 2E
Posts: 51
Joined: Thu Jul 27, 2017 3:00 am
Been upvoted: 2 times

### Re: Initial rates

We use the initial rate because it is the fastest rate and the only time that we know the concentrations of the reactants, since the rate decreases as the reactants are used up.

Simrina Desar Dis 1H
Posts: 49
Joined: Fri Sep 29, 2017 7:04 am

### Re: Initial rates

The curve of the concentration vs time graphs show that as the reaction proceeds, the curves level out... therefore, if you take the rate of the curve later on in the reaction, it will equal 0. This is when the reaction is in more of a thermodynamic setting rather than kinetic. Thus, we take the initial rate since that is when most of the reactants are available to control the reaction.

Masih Tazhibi 2I
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

### Re: Initial rates

We also use the initial values because it makes our calculations a lot simpler. This is because you only have to consider the reactant concentrations, rather than taking into account both products and reactants, as well as the extent of both the forward and reverse reactions.

Jiun Yue Chung 2I
Posts: 27
Joined: Fri Sep 29, 2017 7:06 am

### Re: Initial rates

Also, there may be scenarios where your products are gases and they escape such that the only thing you can accurately rely on to calculate the rate is the reactants themselves.