Question

1. What would be the effect (increase, decrease, no change) on the calculated value of R for each of the following? Explain your reasoning in each case.

a).The vapor pressure of water is neglected in the calculations.

b). Some of the hydrogen gas escaped out the bottom of the tube as it was being generated.

c). Some of the Mg broke loose and floated to the top of the tube, but eventually all reacted.

Answer 1

We know

pV=nRT

Lets write above equation in terms of R

R = pV/nR

a)

When we neglect the vapor pressure of water then pressure H2 gas will be higher than actual value which will increase the value of R as P is at the numerator in above equation.

b)

number of moles of H2 will be less than actual formed and therefore the R value will be less as n is in the denominator

c)

When Mg is reacted completely then no change in the value of n of the H2 formed and therefore there is no any change in R value.