Answer: I disagree. Elements form all pure substances, but some pure substances include elements bonded together to form molecules and compounds.
Explanation:
Pure substances are those that have a uniform and constant (invariable) composition.
That condition is met by both elements and compounds.
Elements are pure substances of one only kind of atoms. For example, gold, oxygen, sodium, hydrogen, are pure substances that arer elements. There are 118 elements known and they are all listed in the periodic table.
Compounds are pure substances formed by two or more different kind of atoms. Water (H₂O), table salt (NaCl), and ethanol (CH₃-CH₂OH), are examples of pure substances that are compounds. There are pratically infinite different compounds.
In conclusion, compounds are also pure substances, since every sample of a given compound has always the same kind of elements bonded in the same way.
Answer is: 4) The same subscripts are on each side of the equation.
For example, balanced chemical reaction:
2Mg + O₂ → 2MgO.
1) The same number of atoms is on each side of the equation: two magnesium atoms and two oxgen atoms.
2) The formulas for all substances are correct: in magnesium oxide (MgO), magnesium has oxidation number +2 and oxygen -2, so formula is good, because compound must be neutral.
3) The same mass is represented on each side of the equation: because there is same number of atoms, the mass is the same.
4) The same subscripts are on each side of the equation: oxygen does not have same subscripts.
Sun, the plants, dwarf plants. you could also say gas giants.
Answer:
Gradual refinement
Explanation:
Gradual refinement is the process whereby the System Development Life Cycle goes through a series of development stages, each stage/phase refining the previous one.
Explanation:
The reaction equation will be as follows.
Using bond energies, expression for calculating the value of 
is as follows.
On reactant side, from 
number of bonds are as follows.
C-C bonds = 1
C-H bonds = 6
From 
; Cl-Cl bonds = 1
On product side, from 
number of bonds are as follows.
C-C bonds = 1
C-H bonds = 5
C-Cl bonds = 1
From HCl; H-Cl bonds = 1
Hence, using the bond energies we will calculate the enthalpy of reaction as follows.
=![[(1 \times 348 kJ/mol) + (6 \times 414 kJ/mol) + (1 \times 242 kJ/mol)] - [(1 \times 348 kJ/mol) + (5 \times 414 kJ/mol) + (1 \times 327 kJ/mol) + (1 \times 431 kJ/mol)]](https://tex.z-dn.net/?f=%5B%281%20%5Ctimes%20348%20kJ%2Fmol%29%20%2B%20%286%20%5Ctimes%20414%20kJ%2Fmol%29%20%2B%20%281%20%5Ctimes%20242%20kJ%2Fmol%29%5D%20-%20%5B%281%20%5Ctimes%20348%20kJ%2Fmol%29%20%2B%20%285%20%5Ctimes%20414%20kJ%2Fmol%29%20%2B%20%281%20%5Ctimes%20327%20kJ%2Fmol%29%20%2B%20%281%20%5Ctimes%20431%20kJ%2Fmol%29%5D)
= -102 kJ/mol
Thus, we can conclude that change in enthalpy for the given reaction is -102 kJ/mol.
