Section 8.2 Law of Conservation of Mass

Vocabulary flashcards covering retrieval, comprehension, analysis, and knowledge utilization questions on the law of conservation of mass, open vs. closed systems, and chemical equation analysis.

Law of Conservation of Mass

A fundamental scientific principle stating that matter cannot be created or destroyed in a chemical reaction, meaning the total mass of the reactants must equal the total mass of the products.

Open System

A system in which matter and energy can freely enter from or escape to the surrounding environment during a reaction or physical process.

Closed System

A system where matter cannot enter or escape into the surroundings, allowing the total mass of substances involved to be contained and measured.

Reactant Mass Calculation (Example 1)

A demonstration of mass conservation where a product of $30\,g$ formed from a first reactant of $17\,g$ requires the second reactant to have a mass of $13\,g$ ($30\,g - 17\,g = 13\,g$).

Product Mass for $35\,g$ of Reactants

The total mass of products formed when $35\,g$ of reactants react to completion, which is exactly $35\,g$.

Product Mass for $12\,g$ of Reactants

The total mass of products formed when $12\,g$ of reactants react to completion, which is exactly $12\,g$.

Product Mass for $2\,g$ and $24\,g$ Reactants

The total product mass resulting from the complete reaction of $2\,g$ of one reactant with $24\,g$ of another reactant, yielding $26\,g$.

Product Mass for $6\,g$ and $3\,g$ Reactants

The total product mass resulting from the complete reaction of $6\,g$ of one reactant with $3\,g$ of another reactant, yielding $9\,g$.

Emma's Experiment (Trial 1 Data)

A trial where $5.90\,g$ of magnesium reacts with $1.74\,g$ of oxygen to produce $7.64\,g$ of product, showing $5.90\,g + 1.74\,g = 7.64\,g$.

Emma's Experiment (Trial 2 Data)

A trial where $2.34\,g$ of magnesium reacts with $1.83\,g$ of oxygen to produce $4.17\,g$ of product, showing $2.34\,g + 1.83\,g = 4.17\,g$.

Emma's Experiment (Trial 3 Data)

A trial where $6.39\,g$ of magnesium reacts with $2.36\,g$ of oxygen to produce $8.75\,g$ of product, showing $6.39\,g + 2.36\,g = 8.75\,g$.

Chemical Equation $C + O_2 \rightarrow CO_2$

A balanced chemical equation that obeys the law of conservation of mass because it has 1 carbon atom and 2 oxygen atoms on both the reactant and product sides.

Chemical Equation $CaCO_3 \rightarrow CaO + CO_2$

A balanced decomposition equation that obeys the law of conservation of mass with equal counts of calcium, carbon, and oxygen atoms on both sides.

Chemical Equation $H_2 + O_2 \rightarrow H_2O$

An unbalanced chemical equation that does not obey the law of conservation of mass as written because there are 2 oxygen atoms on the left and only 1 on the right.

Chemical Equation $Na + Cl_2 \rightarrow NaCl$

An unbalanced chemical equation that does not obey the law of conservation of mass as written because there are 2 chlorine atoms on the left and only 1 on the right.

Chemical Equation $Ba + O_2 \rightarrow BaO$

An unbalanced chemical equation that does not obey the law of conservation of mass as written because there are 2 oxygen atoms on the left and only 1 on the right.

Ideal System for Observing Conservation of Mass

A closed system, because it prevents gaseous products or reactants from escaping into the surrounding environment, allowing all mass to be accounted for.

Apparent Mass Discrepancy in Open Reactions

A situation where $15\,g$ of reactants produce $12\,g$ of measured products; the reaction still obeys conservation of mass because $3\,g$ of product escaped into the air as gas in an open system.

Evaporation Mass Conservation (Paul's View)

The correct explanation for evaporating water in a glass: water mass in the glass decreases because liquid water turns into gas and adds its mass to the surrounding air, rather than mass being destroyed.

Experimental Proof for Water Evaporation

An experiment placing a glass of water inside a sealed, closed container on a balance to demonstrate that the total mass remains constant as the water evaporates into the container's air.