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ehidna [41]
3 years ago
15

Suppose you are investigating the reaction: M(s) + 2 HCl(aq) → MCl2(aq) + H2(g). You weigh out a 0.295 gram piece of metal and c

ombine it with 65 mL of 1.00 M HCl in a coffee-cup calorimeter. If the molar mass of the metal is 57.78 g/mol, and you measure that the reaction absorbed 104 J of heat, what is the enthalpy of this reaction in kJ per mole of limiting reactant? Enter your answer numerically to three significant figures in units of kJ/mol.
Chemistry
1 answer:
Yanka [14]3 years ago
5 0

<u>Answer:</u> The enthalpy of the reaction is 5.30\times 10^{-4}kJ

<u>Explanation:</u>

To calculate the number of moles, we use the equation:

\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}   ....(1)

  • <u>For metal:</u>

Given mass of metal = 0.295 g

Molar mass of metal = 57.78 g/mol

Putting values in above equation, we get:

\text{Moles of metal}=\frac{0.295g}{57.78g/mol}=0.0051mol

  • To calculate the moles of a solute, we use the equation:

\text{Molarity of the solution}=\frac{\text{Moles of solute}}{\text{Volume of solution (in L)}}

We are given:

Volume of hydrochloric acid = 65 mL = 0.065 L   (Conversion factor: 1 L = 1000 mL)

Molarity of the solution = 1 moles/ L

Putting values in above equation, we get:

1mol/L=\frac{\text{Moles of hydrochloric acid}}{0.065L}\\\\\text{Moles of hydrochloric acid}=0.065mol

  • For the given chemical reaction:

M(s)+2HCl(aq.)\rightarrow MCl_2(aq.)+H_2(g)

By Stoichiometry of the reaction:

1 mole of metal reacts with 2 moles of hydrochloric acid..

So, 0.0051 moles of metal will react with = \frac{2}{1}\times 0.0051=0.0102moles of hydrochloric acid.

As, given amount of hydrochloric acid is more than the required amount. So, it is considered as an excess reagent.

Thus, metal is considered as a limiting reagent because it limits the formation of product.

By Stoichiometry of the reaction:

If 1 mole of metal absorbs 104 J of heat

Then, 0.0051 moles of metal will absorb = \frac{104J}{1mol}\times 0.0051mol=0.530J of heat.

Converting joules to kilo joules, we use the conversion factor:

1kJ=1000J

Converting the given value in kilo joules, we get:

\Rightarrow \frac{0.530J}{1000J}\times 1kJ=5.30\times 10^{-4}kJ

Hence, the enthalpy of the reaction is 5.30\times 10^{-4}kJ

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