1. What is the defining characteristic of a closed system in the context of a chemical experiment?
- A. The temperature and pressure inside the system are held constant.
- B. Energy, such as heat and light, is not allowed to enter or exit the system.
- C. The reaction is visible and can be observed from the outside at all times.
- D. Matter, such as atoms and molecules, cannot enter or leave the system.
2. A student burns a piece of wood in a campfire and notices the pile of ash left over is much lighter than the original piece of wood. Why does this not violate the law of conservation of mass?
- A. The law of conservation of mass only applies to reactions in liquids, not to burning solids.
- B. The campfire is an open system, and gaseous products like smoke and carbon dioxide escaped.
- C. A large amount of matter was converted directly into heat and light energy during the fire.
- D. The intense heat of the fire destroyed many of the atoms that made up the wood.
3. If an ice cube is placed in a perfectly sealed, rigid jar and left to melt at room temperature, what will happen to the total mass of the jar and its contents?
- A. The mass will decrease because liquid water is less dense than solid ice.
- B. The mass will increase because energy from the room enters the jar.
- C. The total mass will remain exactly the same.
- D. The mass will first decrease as it melts and then increase as it warms up.
4. In the experiment where steel wool is burned in a sealed jar, the mass of the solid material increases as it forms iron oxide. How is the total mass of the sealed jar conserved?
- A. The mass of the oxygen gas in the jar decreases by an equal amount as it is consumed in the reaction.
- B. The increase in the solid's mass is an illusion caused by the heat of the reaction affecting the scale.
- C. The law of conservation of mass does not apply when there is a change of state from gas to solid.
- D. The jar is not a truly closed system, and air leaks in to balance the mass.
5. Why would a scientist choose to conduct a reaction in a sealed container when trying to verify the law of conservation of mass?
- A. To prevent any gases produced or consumed during the reaction from escaping and affecting the total mass measurement.
- B. To increase the pressure within the container, which forces the reaction to happen more quickly and efficiently.
- C. To ensure the temperature stays perfectly constant, as temperature changes can alter the mass of atoms.
- D. To protect the reactants from being contaminated by microorganisms or dust particles present in the outside air.
6. The scientific principle that matter is not created or destroyed in any chemical or physical change is known as what?
- A. The Theory of Relativity
- B. The Law of Conservation of Mass
- C. The Law of Universal Gravitation
- D. The Principle of Atomic Decay
7. When a puddle of water evaporates on a hot day, it seems to vanish. From a scientific perspective, what has actually happened to the water?
- A. The water has been destroyed.
- B. The water has changed state.
- C. The sun's energy converted the water into air.
- D. The water molecules were broken apart by the heat.
8. A piece of wood is burned in a campfire, leaving only a small pile of ash. What happened to the rest of the wood's matter?
- A. It was permanently destroyed by the heat of the fire.
- B. It transformed into energy and light, ceasing to be matter.
- C. It turned into gases like carbon dioxide and water vapor, which mixed with the air.
- D. It was absorbed into the ground underneath the fire.
9. If you stir a spoonful of salt into a glass of warm water until you can no longer see it, what has happened to the salt?
- A. The salt has been transformed into water molecules.
- B. The water chemically destroyed the salt crystals.
- C. The salt has broken down into particles too small to see and spread throughout the water.
- D. The salt evaporated out of the glass.
10. Which statement best explains why matter seems to 'vanish' during some chemical reactions, like burning a candle?
- A. The matter is being converted directly into heat and light energy.
- B. The solid or liquid reactants are being transformed into invisible gases.
- C. The atoms that make up the matter are being completely annihilated.
- D. The reaction causes the matter to shrink until it is gone.