Laws of Chem­i­cal Com­bi­na­tions Notes

1. Law of Con­ser­va­tion of Mass

• In all phys­i­cal and chem­i­cal changes, there is no net change in mass dur­ing the process.
• Mat­ter can nei­ther be cre­at­ed nor destroyed.

2. Law of Def­i­nite Pro­por­tions

• A giv­en com­pound always con­tains exact­ly the same pro­por­tion of ele­ments by weight.
• The valid­i­ty of this law has been con­firmed by var­i­ous exper­i­ments.
• It is some­times also referred to as Law of Def­i­nite Com­po­si­tion.

3. Law of Mul­ti­ple Pro­por­tions

• If two ele­ments can com­bine to form more than one com­pound, the mass­es of one ele­ment that com­bine with a fixed mass of the oth­er ele­ment are in the ratio of small whole num­bers.

4. Gay Lus­sac’s Law of Gaseous Vol­umes

• When gas­es com­bine or are pro­duced in a chem­i­cal reac­tion, they do so in a sim­ple ratio by vol­ume, pro­vid­ed all gas­es are at the same tem­per­a­ture and pres­sure.

5. Avo­gadro’s Law

• Equal vol­umes of all gas­es at the same tem­per­a­ture and pres­sure should con­tain an equal num­ber of mol­e­cules.

6. Dal­ton’s Atom­ic The­o­ry

• Mat­ter con­sists of indi­vis­i­ble atoms.
• All atoms of a giv­en ele­ment have iden­ti­cal prop­er­ties, includ­ing iden­ti­cal mass. Atoms of dif­fer­ent ele­ments dif­fer in mass.
• Com­pounds are formed when atoms of dif­fer­ent ele­ments com­bine in a fixed ratio.
• Chem­i­cal reac­tions involve the reor­ga­ni­za­tion of atoms. These are nei­ther cre­at­ed nor destroyed in a chem­i­cal reac­tion.

7.Atom­ic and Mol­e­c­u­lar Mass­es

• Atom­ic Mass: The mass of an atom of a chem­i­cal ele­ment expressed in atom­ic mass units (amu).
• Mol­e­c­u­lar Mass: The sum of the atom­ic mass­es of all atoms in a mol­e­cule of the sub­stance.

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