Sunday, April 6, 2014

Magnesium reacts with hydrochloric acid. Which solution would give the fastest initial rate of reaction? a. 40g of HCl in 1000cm3 of water...

There are several factors that affect the rate of a chemical reaction. Concentration of reactants is one. Answer choice C represents the most concentrated solution of HCl. Here are the concentrations, in molarity, of each choice:


A. 40 g HCl X (1 mole/36.5 g) = 1.1 moles


    1.1 moles/1 L = 1.1 M


B. 20 g HCl x (1 mole/36.5 g) = 0.55 moles


    0.55 moles/1 L = 0.55 M


C....

There are several factors that affect the rate of a chemical reaction. Concentration of reactants is one. Answer choice C represents the most concentrated solution of HCl. Here are the concentrations, in molarity, of each choice:


A. 40 g HCl X (1 mole/36.5 g) = 1.1 moles


    1.1 moles/1 L = 1.1 M


B. 20 g HCl x (1 mole/36.5 g) = 0.55 moles


    0.55 moles/1 L = 0.55 M


C. 10 g HCl x (1 mole/36.5 g) = 0.27 moles


    0.27 moles/0.1 L = 2.7 M


D. 4 g HCl x (1 mole/36.5g) = 0.11 moles


    0.11 moles/0.05 L = 2.2 M


You can see from these calculations that choice C has the highest molarity, 2.7 M.


The conversion for g of water to liters is 1000g = 1000ml =1 L, because water has a density of 1.00 g/ml at 25ºC.


Since solution C is the most concentrated, it will initially have more collisions between H+ ions in solution and magnesium ions compared to the other choices. More frequent collisions results in a higher rate of reaction.

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