Chemical Reactions Review

How is a chemical change different than a physical change?

• Chemicals are used.

• The change can be seen but in a physical change it cannot.

• A new substance is formed and in a physical change no new substance is formed.

• Molecules do not physically touch.

In a chemical reaction

• The atoms of the reactants unbond, atoms rearrange, and then rebond to form the products.

• The atoms of the reactants always stay together to form the products.

• New atoms are formed which combine to make the products.

• Some atoms disappear while others multiply to form the products.

What happens in an endothermic reaction?

• Thermal energy is released and the temperature of the products increases.

• Thermal energy is absorbed and the temperature of the products decreases,

• A physical change occurs.

• No new substance is formed.

What happens in an exothermic reaction?

• Thermal energy is absorbed and the temperature of the products decreases.

• Thermal energy is absorbed and the temperature of the products remains constant.

• Thermal energy is released and the temperature of the products increases.

• Thermal energy is released and the temperature of the products does not change..

In a chemical reaction mass is conserved. What does that mean?

• The mass of the reactants stay the same during the chemical reaction.

• The mass of the products stay the same during the chemical reaction.

• The type of atoms, number of atoms, and mass of the reactants equals the type of atoms, number of atoms, and mass of the products..

• The mass of the products is always twice the mass of the reactants.

CH_{4 +} 2 O₂ produces CO_{2 +} 2 H₂O

• 4 carbon atoms, 4 hydrogen atoms, and 2 oxygen atoms

• 1 carbon atom, 4 hydrogen atoms, and 2 oxygen atoms

• 4 carbon atoms, 4 hydrogen atoms, and 4 oxygen atoms

• 1 carbon atom, 4 hydrogen atoms, and 4 oxygen atoms.

Propane + oxygen produces carbon dioxide + water

What are the reactants?

• propane and oxygen

• oxygen and carbon dioxide

• carbon dioxide and water

• water and oxygen

Propane + oxygen produces carbon dioxide + water

What are the products?

• Propane and oxygen

• carbon dioxide and water

• oxygen and carbon dioxide

• oxygen and water

What is the purpose of a catalyst in a chemical reaction?

• To stop the reaction.

• To create more reactants.

• To warm up the reaction.

• To speed up the reaction.

If the total mass of the reactants measures 125 grams, what would be the total mass of the products?

• 250 g

• 125 g

• 50g

• 75 g