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Need help with kinetics question

A large excess of zinc was added to 100cm3 of 0.2 M hydrochloric acid. After the reaction had ended, 240 cm3 of hydrogen had been formed. In three further experiments, extra substances were added to the original mixture as shown in the table below. Fill in the table to show the total volume of hydrogen formed in each experiment and the qualitative effect of these additions on the initial rate of reaction compared to the original experiment.

Substances added to an excess of zinc

100 cm3 water
10g zinc
50 cm3 0.2 M HCL

For each one you have to say how much hydrogen gas produced (in cm3)

The answer to the third one down is 360 but i don't know how to get to that

CAN ANYONE EXPLAIN thanks :smile:
2HCl + Zn --> ZnCl2 + H2

adding water only changed the concentration of HCl, the number of moles didn't change so the amount of hydrogen gas would still be the same.

since the zinc was in excess anyway, adding more zinc won't change anything.

adding more HCl means you'll get more hydrogen gas.
for the sake of simplicity, since the number of mol is the same let's just consider the volume. in the initial experiment you have 100 mL of it, since you add 50 mL more, you have 150% of what you had in the first experiment. so the volume of hydrogen is 150%*240=360

if you need further explanation please quote me.
Reply 2
Avatar for splendidsun
splendidsun
OP
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Original post by desy.kris
2HCl + Zn --> ZnCl2 + H2

adding water only changed the concentration of HCl, the number of moles didn't change so the amount of hydrogen gas would still be the same.

since the zinc was in excess anyway, adding more zinc won't change anything.

adding more HCl means you'll get more hydrogen gas.
for the sake of simplicity, since the number of mol is the same let's just consider the volume. in the initial experiment you have 100 mL of it, since you add 50 mL more, you have 150% of what you had in the first experiment. so the volume of hydrogen is 150%*240=360

if you need further explanation please quote me.


Thanks, explained very well :smile:
oh wait, for the third case I meant the concentration was the same, not the number of mol :P
Reply 4
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splendidsun
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Original post by desy.kris
oh wait, for the third case I meant the concentration was the same, not the number of mol :P


But the concentration isn't the same, the moles are
Original post by splendidsun
But the concentration isn't the same, the moles are


but they're both 0.2 M :/
0.2 M means 0.2 molar, not 0.2 moles. M (molar) refers to the concentration :smile:
Reply 6
Avatar for splendidsun
splendidsun
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Original post by desy.kris
but they're both 0.2 M :/
0.2 M means 0.2 molar, not 0.2 moles. M (molar) refers to the concentration :smile:


wow, makes more sense

thanksss

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