SECTION A
In a chemical equation, what do the subscripts (the small numbers) represent?
A. The number of molecules present. B. The number of atoms of a specific element in a formula.
C. The state of matter (solid, liquid, or gas). D. The speed at which the reaction occurs.
B. The number of atoms of a specific element in a formula.
Which statement best describes the Law of Conservation of Mass?
A. The number of molecules must stay the same in a reaction.
B. The total mass of products is always greater than the reactants.
C. Atoms are neither created nor destroyed, only rearranged.
D. Energy is lost as heat, reducing the total mass of the system.
C. Atoms are neither created nor destroyed, only rearranged.
What number is placed before a chemical formula to balance a chemical equation?
Coefficient
When balancing a chemical equation, what should NOT be changed?
Chemical Formulas (Subscripts)
A student observes that a magnesium ribbon reacts faster in 2.0M Hydrochloric acid than in 0.5M Hydrochloric acid. Which factor is being tested?
A. Temperature B. Catalyst C. Surface Area D. Concentration
D. Concentration
3. In a balanced chemical equation, what must be equal on both sides of the equation?
A. The number of compounds B. The number of atoms of each element
C. The number of molecules D. The number of coefficients
B. The number of atoms of each element
Why does the total mass remain the same after a chemical reaction?
A. New atoms are produced. B. Some atoms disappear.
C. Atoms are rearranged into new substances. D. Products always weigh less.
C. Atoms are rearranged into new substances.
7. During a science fair, two students performed the same experiment by mixing vinegar and baking soda.
After the reaction, Group A measured a lower mass than before the reaction, while Group B measured the same mass before and after the reaction. Which explanation best accounts for the difference?
A. Group A destroyed some of the atoms during the reaction.
B. The carbon dioxide gas escaped from the open cup, while it remained inside the sealed bottle.
C. More atoms were produced in the sealed bottle.
D. The sealed bottle increased the total mass of the products.
B. The carbon dioxide gas escaped from the open cup, while it remained inside the sealed bottle.
In the equation (on the board) , how many atoms of Silver (Ag) are in the product side?
2
Which of the following is an example of a factor that increases the rate of a chemical reaction?
A. Decreasing the temperature. B. Decreasing the surface area of reactants.
C. Increasing the concentration of reactants. D. Adding an inhibitor.
C. Increasing the concentration of reactants.
In a chemical equation, the substances written before the arrow are called:
Reactant
. A balanced chemical equation shows that the number of atoms of each element is the same on both sides of the equation. What does this indicate?
A. Some atoms are destroyed during the reaction.
B. New elements are formed during the reaction.
C. Matter is conserved because atoms are rearranged but not created or destroyed.
D. The products always contain more atoms than the reactants.
C. Matter is conserved because atoms are rearranged but not created or destroyed.
A science teacher wants to demonstrate the Law of Conservation of Mass during a classroom experiment. Four students suggest different experimental setups. Which student designed the best experiment to accurately demonstrate the law?
A. Burn a candle in an open room and compare its mass before and after burning.
B. Mix vinegar and baking soda in a sealed flask, then measure the total mass before and after the reaction.
C. Dissolve sugar in a glass of water and taste the solution.
D. Heat a metal strip until it glows and measure only the strip after heating.
B. Mix vinegar and baking soda in a sealed flask, then measure the total mass before and after the reaction.
If 10 grams of reactant A reacts completely with 5 grams of reactant B, what is the total mass of the products?
15 grams
What is the primary purpose of a catalyst in a chemical reaction?
A. To increase the yield of the product. B. To provide more energy to the reactants.
C. To lower the activation energy required for the reaction. D. To change the state of the products.
C. To lower the activation energy required for the reaction.
To satisfy the Law of Conservation of Mass, what coefficient must be placed before ? (on the board)
2
A chemical company produces water by combining hydrogen gas and oxygen gas. The reaction is shown below: (on the board)
An engineer explains that balancing the equation is important before production begins. Why is balancing the
equation necessary?
A. It ensures that the number of atoms of each element is the same before and after the reaction.
B. It makes the reaction occur faster.
C. It changes hydrogen into oxygen.
D. It increases the amount of products formed without using more reactants.
A. It ensures that the number of atoms of each element is the same before and after the reaction.
. Why does food spoil slower when placed inside a refrigerator?
A. Cold temperatures kill all bacteria instantly.
B. The concentration of oxygen is lower in the fridge.
C. Lower temperatures decrease the kinetic energy of particles, slowing the reaction.
D. The dark environment prevents light-activated decay.
C. Lower temperatures decrease the kinetic energy of particles, slowing the reaction.
A coastal town has two steel bridges.
After several years, Bridge B shows much more rust than Bridge A. Which conclusion best explains this observation?
A. Paint acts as a protective barrier that slows the chemical reaction between iron, oxygen, and moisture.
B. Paint makes the bridge heavier, preventing rust.
C. Rust forms only on unpainted bridges because paint creates new iron atoms.
D. Painted bridges are always built with stronger metals.
A. Paint acts as a protective barrier that slows the chemical reaction between iron, oxygen, and moisture.
Nitrogen-fixing bacteria in the soil use enzymes to turn atmospheric nitrogen into ammonia at room temperature. Without these enzymes, this would require massive heat and pressure. The enzymes are acting as: A. Reactants
B. Products
C. Catalysts
D. Solvents
C. Catalysts
Balance the following equation for the formation of ammonia: (on the board)
(on the board)
A chemical engineer is preparing a safety manual for new workers. The manual must include a balanced equation so workers know the correct proportions of reactants. Which equation should the engineer include? (on the board)
on the board
The city government plans to reduce the corrosion of steel playground equipment near the coast. The engineering team proposes four maintenance plans. Which plan would be the best long-term solution based on factors affecting reaction rates?
A. Coat the steel with rust-resistant paint and inspect it regularly.
B. Spray the steel with saltwater every week.
C. Heat the steel every afternoon to remove moisture.
D. Scratch the paint every month to check for rust.
A. Coat the steel with rust-resistant paint and inspect it regularly.
A company claims that their "Oxygen-Absorber" packets used in dried mango packaging use "chemicals to stop time." Scientifically, what are these packets actually doing?
A. They are cooling the food down to absolute zero.
B. They are removing a reactant (Oxygen), effectively stopping the oxidation reaction.
C. They are changing the chemical identity of the mango into a new substance.
D. They are inhibitors that change the genetic structure of the food.
B. They are removing a reactant (Oxygen), effectively stopping the oxidation reaction.
write the equation: Magnesium reacts with Oxygen gas to form Magnesium oxide
on the board