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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: AnnaC206 on November 25, 2012, 09:02:08 PM

Title: Enthalpy
Post by: AnnaC206 on November 25, 2012, 09:02:08 PM

The reaction between 0.0356 g of magnesium with an excess of HCl was carried out in an ice calorimeter as used in this lab. The volume of water in the calorimeter decreased by 0.16 mL during the reaction. Calculate the enthalpy of the reaction.

I've calculated the moles of mg (1.47 x 10^-3) and moles of water (8.9 x 10^-3). I then wrote the reaction out: Mg +HCl --> MgCl + H2. And since HCl was in excess, everything that reacted was 1.47 x 10^-3 moles. Then I calculated the enthalpy using heats of reaction. Is this right? I'm confused because it says the decrease of water, while we have HCl. Can someone explain that?

Title: Re: Enthalpy
Post by: Borek on November 26, 2012, 04:13:36 AM

It says "volume decreased" - that means some of the ice melted producing water which has lower volume.

Title: Re: Enthalpy
Post by: AnnaC206 on November 26, 2012, 08:35:58 AM

I still don't understand.