Answer:
9.01%
Explanation:
The following data were obtained from the question:
Mass of sodium nitrate, NaNO3 = 56.5g
Mass of solution = 627g
The percentage composition of sodium nitrate, NaNO3 in the solution can be obtained as follow:
Percentage composition of NaNO3 = Mass of NaNO3/mass of solution x 100
Percentage composition of NaNO3 = 56.5/627 x 100 = 9.01%
Therefore, the percentage composition of sodium nitrate, NaNO3 in the solution is 9.01%
<span>I'm assuming its cause the total mass is the same, changes between phases are physical... solid ice and liquid water have the same mass</span>
Answer:
B) ) –1615.1 kJ mol^–1
Explanation:
since
SiO2(s) + 4 HF(aq) → SiF4(g) + 2 H2O(l) ∆Hºrxn = 4.6 kJ mol–1
the enhalpy of reaction will be
∆Hºrxn = ∑νp*∆Hºfp - ∑νr*∆Hºfr
where ∆Hºrxn= enthalpy of reaction , ∆Hºfp= standard enthalpy of formation of products , ∆Hºfr = standard enthalpy of formation of reactants , νp=stoichiometric coffficient of products, νr=stoichiometric coffficient of reactants
therefore
∆Hºrxn = ∑νp*∆Hºfp - ∑νr*∆Hºfr
4.6 kJ/mol = [1*∆HºfX + 2*(–285.8 kJ/mol)] - [1*(–910.9kJ/mol) + 4*(–320.1 kJ/mol)]
4.6 kJ/mol =∆HºfX -571.6 kJ/mol + 2191.3 kJ/mol
∆HºfX = 4.6 kJ/mol + 571.6 kJ/mol - 2191.3 kJ/mol = -1615.1 kJ/mol
therefore ∆HºfX (unknown standard enthalpy of formation = standard enthalpy of formation of SiF4(g) ) = -1615.1 kJ/mol
I can describe one prop. of energy: it can not be created or destroyed. It can be transferred, or converted, though.
