Question

1. choose the best answer.

when a substance changes in a way that does not change its composition, a ______ change has occurred.
slow
physical
fast
chemical

1. choose all that apply.

which three descriptions are properties of water?
water is nonpolar.
water is clear.
water boils at 0 °c.
water has poor thermal conductivity.
water is polar.

Explanation:

1. For question 14:

A physical change is a change in which the substance's composition remains the same. For example, melting ice (solid - liquid change) is a physical change as it is still \(H_2O\). A chemical change would involve a change in composition (e.g., burning wood, where new substances like \(CO_2\) are formed). The speed (slow or fast) is not the defining characteristic of the type of change (physical or chemical).

1. For question 15:

• Water (\(H_2O\)) is a polar molecule because of the bent shape and the difference in electronegativity between \(O\) and \(H\) (\(O\) is more electronegative).
• Water is clear, which is an observable property.
• Water has poor thermal conductivity compared to metals. For example, it takes time for water to heat up throughout a pot.
• Water boils at \(100^{\circ}C\) (at standard atmospheric pressure), not \(0^{\circ}C\) (\(0^{\circ}C\) is the freezing point).

Answer:

1. B. physical
2. B. Water is clear, D. Water has poor thermal conductivity, E. Water is polar