Chemistry is essential in understanding various materials and their interactions.
Significance of chemistry in daily life, including the chemicals we use.
Basic Concepts
Significant Figures: The digits in a number that contribute to its precision.
Elements: Pure substances that cannot be broken down into simpler substances.
Mixtures: Combinations of two or more substances that retain their individual properties.
Chemical Combination: The process where substances combine to form new compounds.
Laws of Chemical Combination
There are 5 major laws governing how elements combine and form compounds.
These laws dictate how elements react, their mass ratios, and the proportions of gases formed.
1. Law of Conservation of Mass
Proposed in the 1740s-1780s, this law states:
Mass cannot be created or destroyed.
The mass of reactants equals the mass of products in a chemical reaction.
Important Points:
When two compounds combine, they form a new compound with a total mass equal to the sum of the individual masses of the reactants.
Example Reaction: Carbon + Oxygen = Carbon Dioxide
Atomic mass of Carbon (C) = 12
Atomic mass of Oxygen (O) = 16 (for O2 = 32)
Total mass of reactants: 12 (C) + 32 (O) = 44
Mass of products (CO2) = 44
Therefore, 12 + 32 = 44 (Balanced reaction)
Modern Relevance
While the law holds for many reactions, some reactions involve energy transformations where E=mc² applies. However, these laws were established before such concepts were discussed.
Practice Question
Question: 1.5 g of ethane combusts to produce 44 g of CO2 and 2.7 g of H2O. Prove this reaction adheres to the law of conservation of mass.
Steps:
Write the balanced chemical equation for the combustion of ethane.
Calculate the total mass of reactants and compare it with the total mass of products.