Chemical Laws and Principles

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Chemical Laws and Principles

Learning objective

Learning Objectives

the lesson you will calculate density and relate it to mass and volume.

What do you already know about chemical reactions?

Law of Conservation of Mass

Mass is conserved in chemical reactions. No mass is created or destroyed. Importance in stoichiometry.

Law of Definite Proportions

Pure compounds have a fixed composition. Elements combine in a specific mass ratio. Example: Water (H2O) always has 2:16 mass ratio.

Law of Combining Volumes

Gases react in simple volume ratios. Conditions: same temperature and pressure. Example: 1 volume of hydrogen reacts with 1 volume of oxygen.

Avogadro's Law

Equal volumes of gases contain equal number of molecules. Applicable at standard temperature and pressure (STP). Use in calculating moles and gas volumes.

Molar Mass

Mass of one mole of a substance. Expressed in grams per mole. Used in stoichiometric calculations.

Percentage Composition

Calculate the percentage of each element in a compound. Use molar mass for calculations. Example: Find percentage composition of CO2.

Equivalent Mass and Valency

Equivalent mass relates to the mass that reacts with a standard amount of another substance. Valency indicates combining capacity of elements.

Density

Mass per unit volume of a substance. Expressed in grams per cubic centimetre. Calculate using mass and volume.

Definitions

Law of Conservation of Mass: The principle stating that mass is neither created nor destroyed in a chemical reaction. Law of Definite Proportions: A chemical law stating that a given compound always contains the same proportion of elements by mass. Law of Combining Volumes: The principle that gases react in simple whole number ratios by volume under the same temperature and pressure. Avogadro's Law: A principle stating that equal volumes of gases at the same temperature and pressure contain an equal number of molecules. Molar Mass: The mass of one mole of a substance, usually expressed in grams per mole. Equivalent Mass: The mass of a substance that will combine with or displace a fixed amount of another substance. Valency: The combining capacity of an element, typically measured by the number of hydrogen atoms it can combine or displace. Density: The mass per unit volume of a substance, often expressed in grams per cubic centimetre.

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