The speed of a car is 16 meters per second. What is this speed in miles per hour? What is а
this speed in miles per hour? (1.61 km = 1 mile, 60 seconds = 1 minute, 60 minutes = 1 hour)
Select one:
a. 180 miles per hour
b. 58 miles per hour
O c. 7.2 miles per hour
d. 36 miles/hour
e. 360 miles per hour

Conversion Factors:

1.61 km = 1 mile

60 sec = 1 min

60 min = 1 hour

Use dimensional analysis to solve.

× × × ×

= 36 miles/hour

If done properly, you should be left with the units miles/hour

first, consult an activity series chart to determine if al is more reactive than fe. it is, so it will replace the fe. now, one can continue with the problem.

next, make sure you have a correctly balanced equation.

3feo + 2al ==> 3fe + al2o3

now, determine which reactant (feo or al) is in limiting supply.

moles feo present = 125 g x 1 mole/71.8 g = 1.74 moles

moles al present = 25.0 g x 1 mole/26.98 g = 0.927 moles

since from the balanced equation, it take 3 mol feo for every 2 mol al, al will be limiting.

you can determine this simply by dividing moles of each by their coefficient in the balanced equation. for example: 1.74/3 = 0.58 and 0.927/2 = 0.464. al is less, so it is limiting.

finally, using the stoichiometry in the balanced eq. determine mass of fe that can be produced from 0.927 moles of al.

0.927 moles al x 3 moles fe/2 moles al x 55.8 g/mole = 77.6 g

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.