Investigation of Enthalpy Change When Mg is added to HCl

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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?


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


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

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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.



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


 = -0.4184

0.02g Mg (

= 0.0008

-0.4184/0.0008= -523 kJ/mol

  1. (10mL)(4.184)(9°C)=376.56


= -0.37656

0.02g Mg (

= 0.0008

-0.37656/0.0008= -470.7 kJ/mol

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