Atomic radius decreases across a period because valence electrons are being added to the same energy level at the same time the nucleus is increasing in protons. The increase in nuclear charge attracts the electrons more strongly, pulling them closer to the nucleus.
Answer:
0.0300 moles of H₂
Explanation:
The original equation is PV = nRT. We need to change this to show moles (n).
n = 
It's important to convert your values to match the constant (r) in terms of units.
30.0 kPa = 0.296 atm
2500 mL = 2.50 L
27 °C = 300 K
Now, plug those values in to solve:
n = 
- for the sake of keeping the problem clean, I didn't include the units but you should just to make sure everything cancels out :)
Finally, you are left with n = 0.0300 moles of H₂
We have that the total enthalpy of the reaction changes with the quantity of the reactants and it is proportional to them. Also, the reverse of a reaction has the opposite enthalpy. Hence, since we need to multiply by 2, the reactants are double and thus the value of the enthalpy is 2 as big. Also, since we are using the inverse reaction, we must also invert the sign. Thus, for this reaction we must use the value H=572 kJ.
