Over the first 57.0 s of the reaction the concentration of hydrogen (H2) dropped from 1.50 M to 0.323 M. Calculate the average change in concentration of ammonia (∆NH3/ ∆t) , in M/s, over this time interval?

0.021M/s

Explanation:

Rate Average = |ΔConcentration / Δtime| = | Δ[NH₃]/Δt |

=  | 0.323M - 1.50M / 57.0s | = | -0.021M/s | = 0.021M/s

Note: calculation of average rate of reaction should be represented as a positive value representing 'speed' of reaction. Many will argue that speed, or rate can be negative (-), but speed is a scalar quantity that represents change of position over a period of time. Acceleration can be negative (~deceleration) but speed is absolute. For example, if one is moving at a speed of 30mi/hr then its is 30mph or it is not 30mph, but can not be a negative in the context of rate.   If you bring this up, you will be challenged. Good Luck :-)