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4 years ago

What is qcal and how do you find it?

1 answer:

4 0

Hess's Law describes the conservation of energy in chemical reactions, stating that the heat flow of a reaction is equal to the sum of the heat flow of its composite reactions. A calorimeter measures the heat flow by creating a closed-system that contains the reaction. Ideally, a reading from the calorimeter would show the exact change in heat that a given reaction requires; however, the calorimeter absorbs an amount of heat from the system. Calculating the Qcal, the heat of the calorimeter, allows you to adjust your readings to determine the total heat flow of a reaction.

This website will help you to find it:
http://chemistry.tutorvista.com/physical-chemistry/specific-heat-capacity.html?view=simple

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3 years ago

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3 years ago

How many liters of hydrogen gas is produced from 3.712 g of magnesium with 104.2ml of 1.385 mol/L HCL (aq) at SATP? Please show

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Explanation:

Hello,

In this case, the undergoing chemical reaction is:

$Mg+2HCl\rightarrow MgCl_2+H_2$

Next, we compute the reacting moles of each reactants:

$n_{Mg}=3.712gMg*\frac{1molMg}{24.305 gMg}=0.153molMg$

$n_{HCl}=1.385\frac{molHCl}{L}*0.1042L=0.144molHCl$

Then, as magnesium and hydrohloric acid are in a 1:2 molar ratio 0.153 moles of magnesium will completely react with 0.306 moles of hydrochloric acid yet we only have 0.144 moles, therefore, limiting reactant is hydrochloric acid. Thus, we compute the produced moles of hydrogen:

$n_{H_2}=0.144molHCl*\frac{1molH_2}{2molHCl} =0.072molH_2$

Finally, we use the ideal gas equation with T=298K and 1atm (STP conditions) to compute the liters of hydrogen gas:

$PV=nRT\\\\V=\frac{nRT}{P}=\frac{0.072mol*0.082\frac{atm*L}{mol*K}*273K}{1atm}\\ \\V=1.61L$

Best regards.

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3 years ago