Number of atoms : 1.26 x 10²³
<h3>Further explanation </h3>
The mole is the number of particles(molecules, atoms, ions) contained in a substance
1 mol = 6.02.10²³ particles
Can be formulated
N=n x No
N = number of particles
n = mol
No = Avogadro's = 6.02.10²³
0.21 moles of Al, so n = 0.21
Number of atoms :

I got b 5)A sample of pure sodium-24 has an initial mass of 10.0 grams. How many grams of sodium-24 will remain at the end of 4 half-lives?
A. 0.315
B. 0.630
C. 5.00
D. 6.00
Use the formula in terms of half life from the normal exponential functions
<span>
N(t) = N(0) (1/2) ^ (t/thalf) </span>
<span>
N(0) is the original quantity </span>
<span>
N(t) = quantity remaining at time t </span>
<span>
t is the time </span>
<span>
thalf is half life </span>
<span>
1/16 = (1/2)^(t/3.82) </span>
<span>
16 = 2^(t/3.82) </span>
<span>
4 = t/3.82 </span>
<span>
t = 15.28 days
I hope my answer has come to your help. Thank you for posting your question here in Brainly. We hope to answer more of your questions and inquiries soon. Have a nice day ahead!
</span>
Answer : The standard enthalpy of formation of ethylene is, 52.4 kJ
Explanation :
According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.
According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.
The formation reaction of
will be,

The intermediate balanced chemical reaction will be,
(1)

(2)

(3)

Now we will reverse the reaction 1, multiply reaction 2 and 3 by 2 then adding all the equation, we get :
(1)

(2)

(3)

The expression for enthalpy of formation of
will be,



Therefore, the standard enthalpy of formation of ethylene is, 52.4 kJ
Answer:
what? that's 66 total, 6 more elliptical machines, a 1 to 1.2 ratio
but I don't know what else you would mean