which formula represents a double displacement reaction?
ca(oh)2(s) mc009-1.jpg cao(s) + h2o(g)
c2h5oh(i) + o2(g) mc009-2.jpg co2(g) + h2o(g)
zn(s) + 2hcl(aq) mc009-3.jpg zncl2(aq) + h2(g)
pb(no3)2(aq) + 2hcl(aq) mc009-4.jpg 2hno3(aq) + pbcl2(s)

Explanation: 1.

This is an example of decomposition reaction in which one reactant gives two or more than two products on absorption of energy.

2.

This is an example of combustion reaction in which hydrocarbon burns in the presence of oxygen to form carbon dioxide, water and energy.

3.

This is an example of single replacement reaction in which a more reactive element displaces a less reactive element from its salt solution.

4.

This is an example of a double displacement reaction in which exchange of ions take place.

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