A sample of crushed rock is found to have 4.81 x10^21 atoms of gold, how many moles of gold are present in this sample? a) 7.99 x 10^-3 moles
b) 1.57 x 10^-1 moles
c) 1.25 x 10^3 moles
d) 2.47 x 10^5 moles

0.8 moles

Explanation:

To find the number of moles in a substance given it's number of entities we use the formula

\begin{gathered}n = \frac{N}{L} \\\end{gathered}

n=

L

N

where n is the number of moles

N is the number of entities

L is the Avogadro's constant which is

6.02 × 10²³ entities

We have

\begin{gathered}n = \frac{4.81 \times {10}^{23} }{6.02 \times {10}^{23} } = \frac{4.81}{6.02} \\ = 0.799003...\end{gathered}

n=

6.02×10

23

4.81×10

23

=

6.02

4.81

=0.799003...

We have the final answer as

0.8 moles

Hope this helps you

answer: the value of enthalpy change will be -152.80 kj.

solution:

pressure = 1atm , temperature = = 298 k

given that pressure and temperature are same in both gases , the number of moles of both gases can be determined by the ideal gas equation.

according to reaction 3 moles no are reacting with 1 mol of ,then 0.49 mol of no will react with moles of ozone that is 0.16 moles of ozone. since, no is limiting reagent and is an excessive reagent.

enthalpy change for the reaction between the given volumes of the gases is :