Matter, Atoms, and the Law of Conservation of Mass

Matter

• Matter is anything that has mass, takes up space, and can exist as a solid, liquid, or gas
• The amount of matter contained in an object is its mass

Elements and Atoms

• Ancient Greeks theorized that all living things consisted of four basic "elements": earth, air, fire, and water
• An element today is a substance that cannot be broken down into other substances, like gold or calcium
• The atom is the smallest unit of an element; it retains all the characteristics of that element

The Law of Conservation of Mass

• Mass in a closed system cannot be created or destroyed
• During chemical reactions, mass of the components remains constant
• Though constituent parts reconfigure, atoms involved are simply rearranged, mass is conserved
• For example, wood (cellulose) reacting with oxygen in a fire yields an equal number of atoms in different forms, like carbon dioxide gas, water vapor, and charcoal ash

Acids and Bases

• Acids and bases are characterized by their interactions with water
• Acids yield positively charged hydrogen ions (H+) when dissolved in water
• Bases produce negatively charged hydroxide ions (OH-)
• Bases reduce the presence of hydrogen ions (H+) when dissolved in water
• The pH scale, ranging from 0-14, measures the strength of acidic and basic solutions
• A pH below 7 indicates acidity, while a pH above 7 indicates a base

Phase Change

• Matter can undergo phase changes
• Examples include changing from solid to liquid to gas without altering its chemical composition, e.g., ice, water and vapor
• Gases experience pressure changes due to continuous collisions of rapidly moving molecules in a closed container
• Examples include car tired or blimps
• Differences in the organization of molecules dictate whether a state of matter is solid, liquid, or gas, and variations in heat and pressure cause such phase changes

Energy

• Energy is present in the universe in forms of heat, light, and motion
• Defined, energy is the capacity to do work
• Work involves applying force to an object across a distance
• Kinetic energy is possessed by something that is in motion, such as water turning a turbine
• Potential energy is stored in something that has yet to be released, such as water being held behind a dam

Thermodynamics

• The First Law of Thermodynamics: energy, like matter, is a constant in the universe, meaning it cannot be created or destroyed
• The Second Law of Thermodynamics: during energy transfer, energy degrades and dissipates in the form of heat
• Tendency of any isolated system to become disordered such that the system's entropy (a measure of disorder) increases
• Energy conversions are never 100% efficient because of entropy

Energy Transfer

• Ecologists classify living things by their trophic levels, which indicate their position in the food chain
• Plants, algae, and some bacteria are primary producers, and they are able to convert sunlight into chemical energy via photosynthesis
• Organisms that consume these producers directly are primary consumers
• Approximately 10% of energy from consumed organic matter is transferred to the next trophic level, accounting significant energy loss