The statement is false because endothermic reactions have a positive enthalpy change, because heat is being added to the system because it requires more energy to react
The atomic mass of element is the weighted average atomic mass of the element with respect to the abundance of the isotopes of that element
atomic mass is the sum of the products of the mass of isotopes by their percentage abundance
atomic mass = 15.000 amu x 5.000 % + 16.000 amu x 95.000 %
= 0.7500 + 15.200
atomic mass of element is therefore 15.950
4X + 3O₂ = 2X₂O₃
n(X₂O₃)=0.02225 mol
m(X)=4.000 g
x - the molar mass of metal
m(X)/4x=n(X₂O₃)/2
x=m(X)/{2n(X₂O₃)}
x=4.000/{2*0.02225)=89.89 g/mol
X=Y (yttrium)
To separate oil from water, add a solution of soluble ionic salt to the solution. Distillation, which involves boiling and condensing the water, is another option, as well as partially freezing the oil and water combination and discarding one-fourth to one-third of the unfrozen water.
<span>The combining of two atomic nuclei to produce one larger nucleus is called nuclear fusion. </span>
