Physical vs. Chemical Changes
Question: Why is melting ice considered a physical change rather than a chemical change?
Answer: The substance remains H₂O and no new substance is formed.
Question: How does a solvent differ from a solute in a solution?
Answer: The solvent dissolves the solute and is usually present in greater amount.
Question: What does the slope of a distance–time graph represent?
Answer: The speed of the object.
Question: What does Newton’s First Law say about objects in motion?
Answer: An object in motion stays in motion unless acted on by an unbalanced force.
Question: Why does thermal energy always move from warmer objects to cooler objects?
Answer: Particles with higher kinetic energy transfer energy to slower-moving particles.
Question: What evidence distinguishes a chemical change from a physical change at the particle level?
Answer: Chemical changes rearrange atoms to form new substances; physical changes do not.
Question: Why is water considered the universal solvent?
Answer: It can dissolve more substances than most other liquids.
Question: Why does a horizontal line on a distance–time graph indicate zero speed?
Answer: Distance does not change over time, meaning the object is not moving.
Question: How does mass affect inertia?
Answer: Objects with more mass have greater inertia.
Question: How is conduction different from convection at the particle level?
Answer: Conduction transfers energy through direct contact; convection transfers energy through fluid movement.
Question: A student observes bubbling when two clear liquids are mixed. Why does this suggest a chemical change?
Answer: The bubbles indicate a gas is being produced, which is evidence of a new substance forming.
Question: How does temperature affect the motion of particles in a solution, and why does this increase solubility?
Answer: Higher temperature increases particle motion, causing more collisions that help solute dissolve.
Question: If two lines start at the same point but one is steeper, what can be concluded about their speeds?
Answer: The steeper line represents a faster-moving object.
Question: Why do passengers move forward when a car stops suddenly?
Answer: Their bodies resist changes in motion due to inertia.
Question: Why does warm air rise in a room?
Answer: Warm air is less dense because particles move faster and spread apart.
Question: Why is dissolving salt in water considered a physical change even though the salt seems to “disappear”?
Answer: The salt particles remain intact and can be recovered by evaporating the water.
Question: Why will sugar dissolve faster in hot water but not dissolve forever?
Answer: Hot water increases dissolving rate, but saturation limits how much can dissolve.
Question: How can you identify an object that changes speed on a distance–time graph?
Answer: The graph is curved or has changing slopes.
Question: Why does a heavy truck require a greater force to stop than a small car moving at the same speed?
Answer: The truck has greater mass and therefore greater inertia.
Question: Why does metal feel colder than wood at the same temperature?
Answer: Metal conducts thermal energy away from your hand faster than wood.
Question: A substance changes color and releases heat but remains the same mass. Explain why this is still a chemical change.
Answer: Color change and energy release indicate a new substance formed despite mass being conserved.
Question: Two solutions contain the same amount of solute, but one dissolves faster. What variable most likely caused the difference?
Answer: Temperature, stirring, or surface area of the solute.
Question: Two objects travel for 10 seconds. One travels farther but has a less steep graph. How is this possible?
Answer: The object traveled longer at a moderate speed, while the steeper graph represents faster speed for a shorter distance.
Question: A puck slides across ice and slows down. Why does this not violate Newton’s First Law?
Answer: Friction is an unbalanced force acting on the puck.
Question: Identify and explain all three heat transfer methods involved when standing near a campfire.
Answer: Radiation from the fire, convection from rising warm air, and conduction through direct contact with heated objects.