## 15.23C

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

Rachel Wang
Posts: 49
Joined: Fri Sep 29, 2017 7:04 am

### 15.23C

The problem states :
Determine the rate constant for each of the following
first-order reactions, in each case expressed for the rate of loss
of A:

But part C) has the rxn equation : (c) 2 A -> B + C

Isn't this a second order, not a first order, rxn in respect to A?

Luke Bricca 1H
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

### Re: 15.23C

The coefficient being 2 doesn't necessarily mean that A is second order. Order is determined by how the rate reacts to changes in reactant concentration, and the coefficient isn't used in determining that. A coefficient could be helpful if [B] or [C] was given and you needed to convert a final concentration of [A].

Sally Nason - 1K
Posts: 40
Joined: Fri Sep 29, 2017 7:05 am

### Re: 15.23C

If the question tells you what order the reaction is in, always go with that because it is directly stated in the question.

Phillip Winters 2F
Posts: 50
Joined: Fri Sep 29, 2017 7:05 am

### Re: 15.23C

The coefficient is not always indicative of the reaction order, the problem may give the order or values the concentration of reactant and rate constant will be given and you must determine order by observing changes in these values

Jacob Cho 2L
Posts: 12
Joined: Fri Sep 29, 2017 7:05 am

### Re: 15.23C

Not necessarily. A second order reaction would have two different reactants. This reaction has two of the same reactant.

Alejandra Rios 1L
Posts: 31
Joined: Fri Sep 29, 2017 7:06 am
Been upvoted: 1 time

### Re: 15.23C

The coefficients in the equation don't have an effect on the order. If the problem says its first-order then the reaction should be able to be worked out using the equations we have for first-order reactions.

Michelle Lu 1F
Posts: 50
Joined: Thu Jul 27, 2017 3:01 am
Been upvoted: 1 time

### Re: 15.23C

You cannot determine the order of a reaction by looking at the coefficients of the reactants or products. However, you can use these coefficients to determine the ratios of the rates for the consumption of reactants or the production of products.