Physical and Chemical Changes

A teacher has two cubes of sugar that are both the same size and shape. He adds cube A to a beaker filled with 100 mL of water, and the cube completely dissolves in the water. He then places cube B on a glass dish over a flame. He keeps the dish over the flame until cube B has turned completely black. Once cube B has cooled off, he adds it to another beaker filled with 100 mL of water. Cube B does not dissolve in water.

What does this demonstration indicate?

• Sugar is a mixture that can be separated by burning it.

• Sugar is a mixture that can be separated by dissolving it in water.

• Dissolving sugar in water results in a chemical reaction.

• Burning sugar results in a chemical reaction.

Tags

NGSS.MS-PS1-2

In the chemical reaction below, calcium (Ca) and water (H₂O) react to form calcium hydroxide (Ca(OH)₂) and hydrogen gas (H₂).

Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

Calcium and water are the reactants in this chemical reaction. The products are calcium hydroxide and hydrogen gas. Which statement correctly describes the total mass of the products when the reaction is complete?

• The total mass of the products cannot be found from the original mass of the reactants.

• The total mass of the products will be greater than the original mass of the reactants.

• The total mass of the products will be less than the original mass of the reactants.

• The total mass of the products will be equal to the original mass of the reactants.

Tags

NGSS.MS-PS1-5

The diagram below shows the reaction between iron oxide and carbon that produces iron and carbon dioxide.

The reaction takes place in a closed system. What is true about the carbon atoms in the reaction?

• The total mass of the carbon atoms is the same as the total mass of the iron atoms.

• The mass of the carbon atoms increases between the reactants and the products of the reaction.

• The total mass of the carbon atoms is the same as the total mass of the oxygen atoms.

• The mass of carbon atoms in the reactants is the same as the mass of carbon atoms in the products.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

When methane undergoes a chemical reaction with oxygen, carbon dioxide and water are formed as products. Which of the following would be the strongest evidence to show that a chemical reaction has occurred?

• Methane and oxygen have different chemical properties.

• The mass of the reactants is the same as the mass of the products.

• Water is usually part of a mixture.

• Methane has a different boiling point than both carbon dioxide and water.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

Which of the following is true about the mass of the reactants in a chemical reaction?

• The total mass of the reactants in a chemical reaction will be significantly more than the total mass of the products.

• The total mass of the reactants in a chemical reaction will always be equal to the total mass of the products.

• The total mass of the reactants in a chemical reaction will be significantly less than the total mass of the products.

• The total mass of the reactants in a chemical reaction will never be equal to the total mass of the products.

Tags

NGSS.MS-PS1-5

The diagram below shows the reaction of oxygen gas and hydrogen gas to form water.

The chemical reaction shown above takes place in a closed system. What is true about the system while the reaction occurs?

• The total mass of the system increases.

• The mass of the oxygen atoms increases.

• The total mass of the system stays the same.

• The mass of the hydrogen atoms decreases.

Tags

NGSS.MS-PS1-5

The following diagram represents the reaction of methane with oxygen gas to form carbon dioxide and water.

The chemical reaction shown above takes place in a closed system. What is true about the system while the reaction occurs?

• The total mass of the particles in the system stays the same.

• The total number of particles in the system decreases.

• The total mass of the particles in the system increases.

• The total number of particles in the system increases.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

According to the law of conservation of matter, which statement about chemical reactions is true?

• Energy is created as atoms are destroyed in chemical reactions.

• Atoms cannot be created or destroyed by chemical reactions.

• Every atom destroyed in a chemical reaction must be replaced.

• Atoms are created by some reactions and destroyed by others.

Tags

NGSS.MS-PS1-5

Juan has eight marbles that are all the same size. He knows that one marble weighs 10 grams. To find out how much his marbles weigh all together, he adds 8 tens and gets a total of 80 grams.

10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 = 80

Why does this method of finding the total weight work?

• he weight of a group is always less than the sum of the weights of all its parts.

• The weight of a group is equal to the sum of the weights of all its parts.

• The weight of a group is not related to the weights of its parts.

• The weight of a group is always greater than the sum of the weights of all its parts.

Cellular respiration describes the process that living cells use to release energy by combining sugar and oxygen. The primary chemical changes that happen during cellular respiration are shown in the equation below.

Which statement correctly compares the reactants and products of the equation?

• The mass of the reactants is the same as the mass of the products.

• The number of reactant atoms is greater than the number of product atoms.

• The mass of the reactants is less than the mass of the products.

• The number of reactant atoms is less than the number of product atoms.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5