Understanding Physical and Chemical Changes

The difference between a physical change and a chemical change is that a chemical change makes a new substance. For example, when water boils, it goes through a physical change, but it does not change into a different substance (it's still water). Choose the three actions that describe physical changes.

• burning wood

• dissolving salt in water

• crushing a pill

• baking bread

• cutting paper

Carlos is building a wooden fence. He saws a large plank of wood into several smaller pieces to fit between the posts. What kind of change is taking place as the wood is sawed?

• a change in chemical composition

• a change in physical property

• a change into a new substance

• a change in chemical property

A researcher is investigating how the concentration of a salt solution affects its freezing point. They prepare four different salt solutions, each with a different salt concentration (5%, 10%, 15%, and 20% salt by mass). They then measure the freezing point of each solution. What is the independent variable in this experiment?

• The freezing point of the solution

• The amount of solution used

• The type of salt used

• The concentration of the salt solution

Ethan is stirring a mug of hot soup with a metal spoon. The spoon begins to feel warm to the touch because thermal energy is transferring from the soup to the spoon. Thermal energy is an example of what type of energy transfer?

• Conduction

• Radiation

• Convection

• Evaporation

Energy naturally flows from _____ matter to _____ matter. Which of the following best completes the sentence?

• Cooler to warmer

• Warmer to cooler

• Same temperature to higher temperature

• Lower temperature to same temperature

Tags

NGSS.MS-PS1-4

During a chemistry class, students observe a reaction that causes the test tube to feel cold to the touch because the reaction is absorbing heat from the surroundings. Which word describes the direction of heat flow illustrated in this scenario?

• Exothermic

• Endothermic

• Thermal

• Physical

Tags

NGSS.MS-PS1-4

• $DEST_1$: products, $DEST_2$: reactants

• $DEST_1$: reactants, $DEST_2$: products

• $DEST_1$: synthetics, $DEST_2$: polymers

• $DEST_1$: elements, $DEST_2$: compounds

Tags

NGSS.MS-PS1-2

A chemist performs a reaction where the total mass of the starting substances is measured as 50 grams. After the reaction is complete, the total mass of the newly formed substances is also 50 grams. This observation supports the law of conservation of mass. According to this law, what happens in a chemical reaction?

• A new kind of matter is created, and the total mass increases.

• Matter is only changed into energy, so the total mass decreases.

• Matter is converted into a gas, making the final mass seem less than the starting mass.

• Matter is not created or destroyed, and the same amount of mass remains.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

Which of the following statements is NOT true about a compound?

• It is a pure substance.

• It can be chemically separated into simpler substances.

• It is made up of only one kind of atom.

• It is made up of two or more different elements chemically bonded together.

A student observes a substance in a beaker. They can clearly see distinct layers and differently colored pieces of material mixed throughout the substance, and it looks unevenly blended. What type of substance is this?

• Element

• Homogeneous mixture (solution)

• Compound

• Heterogeneous mixture