# Investigation of Enthalpy Change When Mg is added to HCl

by kmann561 (student)

Investigation of Enthalpy Change When Mg is added to HCl

Defining the Problem and Selecting Variables

Research Question:

How is the enthalpy change of the reaction between Mg and HCl affected when different amounts of Mg are added to a constant amount of HCl?

Variables:

Independent: Mg

Dependent: Temperature

Control: HCl

Controlling Variables

I will use three different masses of Mg: 0.02g ± 0.001g, 0.03g ± 0.001g, 0.04g ± 0.001g

I will measure the temperature using a colorimeter made from a foam cup, a lid, and a thermometer

I will keep HCl at a constant volume of 10mL of 1M HCl

Procedure:

Step 1:  Measure out 10mL of 1M HCl

Step 2: Pour HCl into foam cup and place lid on cup

Step 3: Measure the initial temperature and record data

Step 4: Add in 0.02g of Mg into cup and measure the finial temperature

Step 5: Calculate change in temperature by subtracting the initial temperature from the finial temperature

Step 6: Repeat steps 1-5 8 more times for a total of 9 trails changing the mass of Mg in step 4 every 3 trails from 0.02g ± 0.001g to 0.03g ± 0.001g to 0.04g ± 0.001g.

Data

Calculations:

When a sample of Mg dissolves in 10mL HCl, the temp increases. The following are the ΔH of the 9 trials:

Equation: q=mcΔT

Trial 1 0.02g ± .001g Mg

1. (10mL)(4.184)(10°C)= 418.4

Qw=

= -0.4184

0.02g Mg (

= 0.0008

-0.4184/0.0008= -523 kJ/mol

1. (10mL)(4.184)(9°C)=376.56

Qw=

= -0.37656

0.02g Mg (

= 0.0008

-0.37656/0.0008= -470.7 kJ/mol