Blueprint MCAT Formerly Next Step
Return to Blog Homepage

PCAT Chemical Processes – Rate Law for Elementary Reaction

  • by Sam
  • Apr 19, 2018
  • PCAT Question of the Day

The reaction CO (g) + NO3 (g) → CO2 (g) + NO2 (g) is an elementary reaction. Which of the following accurately gives the rate law for this process?

Click for Explanation

A is correct. The rate law of an elementary reaction can be determined from examining the balanced reaction. Only reactants are included in rate laws, but products are not, allowing us to eliminate Choices C and D. (Do not confuse rate laws with equilibrium expressions!) Each reactant listed in a rate law should be raised to the power of its coefficient, which is 1 here for both reactants. The 3 in NO3 is a subscript, not a coefficient, so that term should not be cubed (eliminate Choice B).

Submit a Comment