How many atoms are there in 2.43 g of calcium?

Explanation:

We're asked to calculate the number of atoms of

Ca

in

153

g Ca

.

What we must first do is convert the given mass of calcium to moles of calcium, using its molar mass (referring to a periodic table, this is

40.08

g

mol

):

153

g Ca

(

1

mol Ca

40.08

g Ca

)

=

3.82

mol Ca

Using Avogadro's number,

6.022

×

10

23

particles

mol

, we can calculate the number of atoms present:

3.82

mol Ca

(

6.022

×

10

23

atoms Ca

1

mol Ca

)

=

2.30

×

10

24

atoms Ca

answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.