Explain Conservation of Mass - Middle School Physical Science
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What atomic-level statement best explains why mass is conserved during a chemical reaction?
What atomic-level statement best explains why mass is conserved during a chemical reaction?
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Atoms are rearranged; none are created or destroyed. Bonds break and form, but atoms themselves remain unchanged.
Atoms are rearranged; none are created or destroyed. Bonds break and form, but atoms themselves remain unchanged.
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Find the missing coefficient that balances oxygen: $CH_4 + __O_2 \rightarrow CO_2 + 2H_2O$.
Find the missing coefficient that balances oxygen: $CH_4 + __O_2 \rightarrow CO_2 + 2H_2O$.
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$2$. Products have 4O total, so need 2 $O_2$ molecules.
$2$. Products have 4O total, so need 2 $O_2$ molecules.
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Choose the balanced form that conserves atoms: $2CO + O_2 \rightarrow 2CO_2$ or $CO + O_2 \rightarrow CO_2$.
Choose the balanced form that conserves atoms: $2CO + O_2 \rightarrow 2CO_2$ or $CO + O_2 \rightarrow CO_2$.
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$2CO + O_2 \rightarrow 2CO_2$. First has 2C and 4O on each side; second is unbalanced.
$2CO + O_2 \rightarrow 2CO_2$. First has 2C and 4O on each side; second is unbalanced.
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Identify the missing coefficient that balances: $__Al + 3Cl_2 \rightarrow 2AlCl_3$.
Identify the missing coefficient that balances: $__Al + 3Cl_2 \rightarrow 2AlCl_3$.
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$2$. Need 2Al on left to match 2Al in products.
$2$. Need 2Al on left to match 2Al in products.
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What is the correct atomic-level reason a precipitate forming does not violate conservation of mass?
What is the correct atomic-level reason a precipitate forming does not violate conservation of mass?
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Atoms move into a solid; total atoms and mass stay the same. Dissolved atoms reorganize into solid form.
Atoms move into a solid; total atoms and mass stay the same. Dissolved atoms reorganize into solid form.
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Which statement is correct: atoms can be created in chemical reactions, or atoms only rearrange?
Which statement is correct: atoms can be created in chemical reactions, or atoms only rearrange?
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Atoms only rearrange in chemical reactions. Chemical reactions cannot create or destroy atoms.
Atoms only rearrange in chemical reactions. Chemical reactions cannot create or destroy atoms.
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Identify the correct comparison: mass conservation in closed system vs open system with escaping gas.
Identify the correct comparison: mass conservation in closed system vs open system with escaping gas.
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Closed: measured mass constant; open: measured mass may decrease. Open systems lose mass when gas escapes to surroundings.
Closed: measured mass constant; open: measured mass may decrease. Open systems lose mass when gas escapes to surroundings.
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Which option is the correct balanced equation: $2H_2 + O_2 \rightarrow 2H_2O$ or $H_2 + O_2 \rightarrow H_2O$?
Which option is the correct balanced equation: $2H_2 + O_2 \rightarrow 2H_2O$ or $H_2 + O_2 \rightarrow H_2O$?
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$2H_2 + O_2 \rightarrow 2H_2O$. First equation has 4H and 2O on each side; second doesn't.
$2H_2 + O_2 \rightarrow 2H_2O$. First equation has 4H and 2O on each side; second doesn't.
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What must be true about the total number of atoms in a correct particle diagram of a reaction?
What must be true about the total number of atoms in a correct particle diagram of a reaction?
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Total atoms of each element match before and after. Conservation requires identical atom counts on both sides.
Total atoms of each element match before and after. Conservation requires identical atom counts on both sides.
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Which law is being applied when you count atoms in reactants and products to check a model?
Which law is being applied when you count atoms in reactants and products to check a model?
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Law of conservation of mass. This law requires equal atom counts before and after.
Law of conservation of mass. This law requires equal atom counts before and after.
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Identify the missing coefficient to conserve atoms: $__N_2 + 3H_2 \rightarrow 2NH_3$.
Identify the missing coefficient to conserve atoms: $__N_2 + 3H_2 \rightarrow 2NH_3$.
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$1$. Need 2N atoms on left to match 2N in $2NH_3$ on right.
$1$. Need 2N atoms on left to match 2N in $2NH_3$ on right.
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What does “closed system” mean when applying conservation of mass to a reaction?
What does “closed system” mean when applying conservation of mass to a reaction?
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No matter enters or leaves the system. System boundaries prevent mass exchange with surroundings.
No matter enters or leaves the system. System boundaries prevent mass exchange with surroundings.
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What is conserved in a physical change (such as melting) at the particle level?
What is conserved in a physical change (such as melting) at the particle level?
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The same particles remain; only arrangement and motion change. Physical changes don't create or destroy particles.
The same particles remain; only arrangement and motion change. Physical changes don't create or destroy particles.
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Which type of change occurs to atoms during a chemical reaction: identity change or bonding change?
Which type of change occurs to atoms during a chemical reaction: identity change or bonding change?
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Bonding change (atom identities remain the same). Atoms form new bonds but keep their element identity.
Bonding change (atom identities remain the same). Atoms form new bonds but keep their element identity.
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What does it mean if an equation is unbalanced when using atomic-level models?
What does it mean if an equation is unbalanced when using atomic-level models?
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At least one element has different atom counts on each side. Unequal atom counts violate conservation of mass.
At least one element has different atom counts on each side. Unequal atom counts violate conservation of mass.
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Which option describes what coefficients do in a balanced chemical equation?
Which option describes what coefficients do in a balanced chemical equation?
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They change molecule counts to match atom counts. Coefficients multiply molecules to balance atom counts.
They change molecule counts to match atom counts. Coefficients multiply molecules to balance atom counts.
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What does a balanced chemical equation represent at the atomic level?
What does a balanced chemical equation represent at the atomic level?
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Equal counts of each element’s atoms on both sides. Same number of each atom type appears on both sides.
Equal counts of each element’s atoms on both sides. Same number of each atom type appears on both sides.
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What is the difference between conserving mass and conserving the number of molecules in a reaction?
What is the difference between conserving mass and conserving the number of molecules in a reaction?
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Mass and atoms are conserved; molecules may change in number. Atoms recombine into different molecules during reactions.
Mass and atoms are conserved; molecules may change in number. Atoms recombine into different molecules during reactions.
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Which quantity must be the same before and after a chemical reaction to show mass conservation?
Which quantity must be the same before and after a chemical reaction to show mass conservation?
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The number of each type of atom. Each element's atom count must balance to conserve mass.
The number of each type of atom. Each element's atom count must balance to conserve mass.
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What does the law of conservation of mass state for a chemical reaction in a closed system?
What does the law of conservation of mass state for a chemical reaction in a closed system?
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Total mass of reactants equals total mass of products. Matter cannot be created or destroyed in chemical reactions.
Total mass of reactants equals total mass of products. Matter cannot be created or destroyed in chemical reactions.
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What is the best explanation if measured mass seems to decrease during a reaction?
What is the best explanation if measured mass seems to decrease during a reaction?
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A gas likely escaped because the system was not closed. Mass appears lost when products escape as gases.
A gas likely escaped because the system was not closed. Mass appears lost when products escape as gases.
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Identify the conserved quantity in $2 ext{H}_2 + ext{O}_2
ightarrow 2 ext{H}_2 ext{O}$: H atoms, O atoms, or both?
Identify the conserved quantity in $2 ext{H}_2 + ext{O}_2 ightarrow 2 ext{H}_2 ext{O}$: H atoms, O atoms, or both?
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Both H atoms and O atoms are conserved. All atoms must be conserved for mass to be conserved.
Both H atoms and O atoms are conserved. All atoms must be conserved for mass to be conserved.
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What does it mean to balance an equation using atomic-level reasoning?
What does it mean to balance an equation using atomic-level reasoning?
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Adjust coefficients so each element has the same atom count. Balancing preserves atom counts without changing substances.
Adjust coefficients so each element has the same atom count. Balancing preserves atom counts without changing substances.
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Which change is allowed in a balanced equation: changing coefficients or changing subscripts?
Which change is allowed in a balanced equation: changing coefficients or changing subscripts?
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Changing coefficients is allowed; changing subscripts is not. Subscripts define compounds; changing them creates different substances.
Changing coefficients is allowed; changing subscripts is not. Subscripts define compounds; changing them creates different substances.
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What is the meaning of a subscript in a chemical formula at the particle level?
What is the meaning of a subscript in a chemical formula at the particle level?
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It tells the number of atoms of that element in one particle. Subscripts define the chemical identity of compounds.
It tells the number of atoms of that element in one particle. Subscripts define the chemical identity of compounds.
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