Chemical Reactions and Conservation of Mass

• A. The number of carbon atoms is the same on both sides of the equation; the number of hydrogen and oxygen atoms decreases in the products.

• B. The number of carbon, hydrogen, and oxygen atoms is different on both sides of the equation.

• C. The number of carbon and hydrogen atoms is the same on both sides of the equation; the number of oxygen atoms increases in the products.

• D. The number of carbon, hydrogen, and oxygen atoms is the same on both sides of the equation.

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NGSS.MS-PS1-5

Taleah conducts a chemical reaction and wants to know the number of hydrogen atoms in the products. Hydrogen only appears in the compound 2H2O in the reactants. How many hydrogen atoms must be in the products?

• There must be 8 hydrogen atoms in the products, because mass increases from reactants to products.

• There must be 4 hydrogen atoms in the products, because the total mass is conserved.

• There must be 2 hydrogen atoms in the products, because the total mass is conserved.

• There must be 6 hydrogen atoms in the products, because mass decreases from reactants to products.

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NGSS.MS-PS1-5

NGSS.MS-PS1-2

Rachel conducts the following reaction: 2Na + Cl2 → 2NaCl She uses 2 g of sodium (Na) and 3 g of chlorine (Cl₂). How many grams of product would she produce?

• 4 g, because each molecule of NaCl would have a mass of 2 g.

• 1 g, because the mass of chlorine is higher than the mass of sodium and results in a product that has less mass.

• 10 g, because one compound of NaCl would have a mass of 5 g and the reaction produces two compounds of NaCl.

• 5 g, because the number and type of atoms are the same before and after the reaction, so the mass in grams should also be the same.

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NGSS.MS-PS1-5

NGSS.MS-PS1-2

Define the conservation of mass and explain how it applies to the chemical equation and the image.

• The conservation of mass states that mass is neither created nor destroyed in a chemical reaction. It applies to the chemical equation and image by ensuring that the mass of reactants equals the mass of products.

• The conservation of mass states that energy is neither created nor destroyed in a chemical reaction. It applies to the chemical equation and image by ensuring that the energy of reactants equals the energy of products.

• The conservation of mass states that volume is neither created nor destroyed in a chemical reaction. It applies to the chemical equation and image by ensuring that the volume of reactants equals the volume of products.

• The conservation of mass states that atoms are neither created nor destroyed in a chemical reaction. It applies to the chemical equation and image by ensuring that the number of atoms of each element is the same on both sides.

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NGSS.MS-PS1-5

A group of students conducts a chemical reaction during a lab. They mix two substances together in a closed system. During the reaction, they notice the temperature of the substances increases. Would this increase in thermal energy change the mass of the products?

• Yes, the mass of the products will increase.

• No, the mass of the products will remain the same.

• Yes, the mass of the products will decrease.

• No, the mass of the products will change unpredictably.

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NGSS.MS-PS1-5

In a chemical reaction, the atoms in the ​​ (a)   rearrange to form new (b)   . This is why the mass before the reaction ​ (c)   the mass after the reaction.​

• products
• is greater than
• reactants
• is equal to
• is less than

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NGSS.MS-PS1-5

If reaction starts with 20g of reactants it should produce 

• a total of 40g of products
• a total of 10g of products
• a total of 80 g of products
• a total of 20g of products

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NGSS.MS-PS1-5

NGSS.MS-PS1-2

If a chemical reaction such as photosynthesis begins with 6 atoms of carbon (C), how many atoms of carbon (C) should be in the products?

• 12 atoms of carbon (C)
• 6 atoms of carbon (C)
• 3 atoms of carbon (C)
• 2 atoms of carbon (C)

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NGSS.MS-PS1-5

In a reaction A + B ----> C,  reactant A has 5g and product  C has 9g. How many grams does reactant B should have? 

• 4g
• 5g
• 9g
• 14g

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NGSS.MS-PS1-5

Balance this equation:

​ (a)   Fe + ​ (b)   O₂ --> ​ (c)   Fe₂O₃

• 4
• 3
• 2
• 1
• 0

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NGSS.MS-PS1-5

NGSS.MS-PS1-2