What Is the Rate Law?

What is the Rate Law?

T.A.

September 14, 2010

Chemistry 116

Introduction:

The purpose of this experiments was to determine the rate law for the reaction of Mg(s) + 2HCl(g) → H2(g) + MgCl2(aq). The rate law combines the reaction rate (k) and factors that affect rates of a chemical reaction. The rate law is usually found in the form of Rate = k [A]a[B]b[C]c (Bauer et at., 2009). The exponents show the order for the corresponding substance. In order to hold all factors except one constant 3 different experiments were required. To determine the rate law, initial rate was used instead of products, because products cannot be held constant. Using initial rate you can determine the exponents for the rate law. The coefficients in the balanced equations do not determine the exponents.

Reference

Laboratory Inquiry in Chemistry. 2009. What is the Rate Law?, pp. 141-143.

Materials and Methods:

As with any lab, first make sure to follow all the lab safety rules during this investigation. Then start by measuring out ~0.07 g of Mg. Next, measure, calculate and record the surface area of the magnesium strips. Put ~20 mL of 1 M HCl in a beaker and draw out into a syringe. Place the Mg strip in the flask that goes along with the stopper and pressure measuring equipment. Connect the stopper, cable, syringe neck and collection machine to one another. Then place the stopper at the neck of the flask and seal with plastic sealant. Screw the filled syringe into the neck connected to the stopper and release the HCl into the flask. Make sure to pull the syringe back out to return the pressure to its original value. Next, make sure to take pressure measurements (in atms) for 60 seconds in 5 second intervals. Record the data. Repeat this process with ~.035 g of Mg and 1 M HCl, and ~.035 g Mg and 0.5 M HCl. Change the time interval to every 40 seconds for the last trial (because the reaction takes so long). After, use your recorded data to calculate the...