### Negative Sign

Posted:

**Sun Feb 25, 2018 6:01 pm**What is the significance of the negative sign in the equation -1/a delta[A]/delta t?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=145&t=28519

Page **1** of **1**

Posted: **Sun Feb 25, 2018 6:01 pm**

What is the significance of the negative sign in the equation -1/a delta[A]/delta t?

Posted: **Sun Feb 25, 2018 6:20 pm**

The negative sign is so that the rate of your reactants is positive. We want to work with positive reaction rates, so we use the negative sign to make the reactants rate positive. Without the negative sign, we'd end up with a negative value because the [R] is decreasing. The final concentration is smaller than the initial for the reactant, and since rate deals with change in concentration, the rate for the reactants would be negative. We don't want that so we add the negative sign.

Posted: **Sun Feb 25, 2018 10:06 pm**

you are finding the average rate of consumption. So, because the reactants are being consumed the delta A or R is going to be negative. For chemical kinetics, the rate is always going to be positive, hence the negative sign.

Posted: **Sun Feb 25, 2018 10:29 pm**

The rate should always be positive, hence the need for the negative sign.

Posted: **Mon Feb 26, 2018 2:20 pm**

We want the rates to be positive, so if a product is being used up in a reaction, the overall term has to be negative, therefore the negative sign at the front.

Posted: **Mon Feb 26, 2018 4:29 pm**

In order to make the rate positive, the negative sign reverses the negative rate of the product being used up in a reaction.

Posted: **Tue Feb 27, 2018 2:50 pm**

We always want positive rates. Since [R] is decreasing it will be negative, and a negative sign will need to be added to counteract that.

Posted: **Wed Feb 28, 2018 12:56 pm**

The reason why we want rates to be positive is because it is the standard convention. It makes it easier to compare rates of formation and consumption to each other without the distraction of the negative sign. Another way to think about it is that we generally don't report our speed in daily life with negative numbers (which indicates direction), so we don't express rate with a negative number here as well.