Chemical Reactions Review!!!!

In a chemical reaction, what do we call the substances that are there before the reaction happens? The atoms of these substances get used to make the new substances.

• Catalysts

• Products

• Reactants

• Enzymes

Answer explanation

In a chemical reaction, the substances present before the reaction are called reactants. They undergo transformation to form new substances, known as products. Therefore, the correct answer is reactants.

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NGSS.MS-PS1-1

In a chemical reaction, what do we call the substances that are formed after the reaction happens? These substances are made from the atoms of the starting materials.

• Catalysts

• Products

• Reactants

• Enzymes

Answer explanation

In a chemical reaction, the substances formed after the reaction are called products. They are created from the atoms of the starting materials, known as reactants. Therefore, the correct answer is 'Products'.

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NGSS.MS-PS1-5

Which observation best indicates a chemical reaction has occurred?

• Some bubbles collect along on the side of a glass

• A solid appears when to liquids are mixed

• A beaker cracks when dropped

• Steam rising from boiling water

Answer explanation

A formation of a substance that won't dissolve indicates the formation of a product has new properties and that a reaction has occured.

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NGSS.MS-PS1-2

Which of the following is evidence of a chemical reaction?

• Observing a substance melt after heating it to its melting point

• Observing new physical or chemical properties after substances are combined

• Observing a substance disappear when stirred into water

• Observing a material break into smaller pieces when struck with a hammer

Answer explanation

Observing NEW physical or chemical properties after substances are combined, heated, or cooled indicates that a chemical reaction has happened.

It shows that the original substances have transformed into new substances with different characteristics.

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NGSS.MS-PS1-2

Which of the following does not involve a chemical reaction?

• Rust forming on iron

• Ice melting into water

• Wood burning in a fire

• Milk spoiling, chunky style

Answer explanation

Ice melting into water is a physical change, not a chemical reaction, as it only alters the state of water without changing its chemical composition. The other options involve chemical reactions that change the substances involved.

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What happens during a chemical reaction?

• Bonds break in the products, forming new reactants.

• New substances form due to the rearrangement of atoms.

• Some atoms in the reactants disappear entirely.

• No energy is ever released or absorbed.

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If bubbling or fizzing occurs during a reaction and the temperature does not change, what does this indicate?

• The reaction caused a temperature change.

• A gas is being produced as a product of the reaction.

• A solid is forming in the liquid.

• The liquid is undergoing a physical change to form a gas.

Answer explanation

Bubbling or fizzing, especially without any added heat, confirms that a gas has been formed as a product

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NGSS.MS-PS1-2

Which two of the following are examples of chemical reactions?

• Spinning a colorful pinwheel so the colors appear to blend

• Steel wool burning leaving behind a bluish residue

• Painting a canvas with paint

• A liquid changing color from blue to red when lemon juice is added

Answer explanation

Steel wool burning is a chemical reaction that produces new substances, while the color change with lemon juice indicates a chemical reaction due to pH change. The other options are physical changes, not chemical reactions.

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What changes when a chemical reaction occurs?

• Mass

• The type of atoms involved

• The arrangement of atoms

• The state of matter only

Answer explanation

In a chemical reaction, the arrangement of atoms changes as they bond differently to form new substances.

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In chemical reactions:

• You break bonds then make bonds

• The atoms gain protons

• Electrons are produced

• Elements are broken down

Answer explanation

In chemical reactions, the process involves breaking existing bonds between atoms and then forming new bonds. This is why the correct answer is 'You break bonds then make bonds', as it accurately describes the sequence of events.

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