Question

what do these two changes have in common?
water evaporating from a lake
snowflakes forming in a cloud
select all that apply.
both are caused by heating. both are changes of state.
both conserve mass. both are chemical changes.

Explanation:

• Changes of state: Water evaporating from a lake is a change from liquid to gas (vaporization). Snowflakes forming in a cloud is a change from gas (water vapor) to solid (deposition). Both are physical changes involving a change in the state of matter.
• Conservation of mass: In any physical change (like changes of state), mass is conserved. The law of conservation of mass states that mass is neither created nor destroyed in a chemical or physical process. For water evaporating, the mass of water vapor is equal to the mass of the liquid water that evaporated. For snowflake formation, the mass of the snowflakes (solid) is equal to the mass of the water vapor that condensed and then solidified.

• Not caused by heating: Snowflake formation is a result of cooling (water vapor in the cloud cools and undergoes deposition to form ice - crystals/snowflakes).
• Not chemical changes: Chemical changes involve the formation of new substances with new chemical properties. In both water evaporation and snowflake formation, the substance remains water (\(H_2O\)) at the molecular level. Only the physical state changes.

Answer:

Both are changes of state. Both conserve mass.