Chemical Reactions CAST Review

The diagrams shown show possible chemical reactions. The different-shaded circles represent different kinds of atoms. When circles are touching, that indicates that those atoms form a molecule. Which representation is a possible chemical reaction?

• A

• B

• C

Answer explanation

According to the law of conservation of atoms, the atoms on the left must equal the same number of atoms on the right. In "C",this is true.

Tags

NGSS.MS-PS1-1

NGSS.MS-PS1-2

NGSS.MS-PS1-5

In class, a group of students added water to two mystery substances and allowed the water to evaporate. They recorded their observations in their notebooks. Which crystal represents Sample A?

• Alum

• Citric Acid

• Epsom Salts

• Sodium Chloride

Tags

NGSS.MS-PS1-2

What is the difference between the substances represented by the symbols Co and CO?

• They are two different ways to represent the element cobalt.

• One is the symbol for an element, and one is a formula for a compound.

• Co represents the element cobalt, and CO represents the element copper.

• They represent two substances, each made up of two elements.

Answer explanation

Tags

NGSS.MS-PS1-1

A student mixes a white solid and a clear liquid together. Which observations are evidence that a chemical reaction occurred?

• The mixture begins to bubble or fizz.

• The mixture changes from white to orange.

• The mixture begins to smoke.

• The mixture gets warm.

Answer explanation

Tags

NGSS.MS-PS1-2

A group of students mixed two liquids together. After leaving the mixture alone for ten minutes, two separate layers formed. They recorded information about each substance in a table. Which piece of evidence supports the claim that a chemical reaction did occur?

• Liquid 1 and layer B have the same boiling point.

• The substance bubbled after liquids 1 and 2 were mixed together and there was a color change.

• The combined mass of liquids 1 and 2 is the same as the combined mass of layer A and layer B plus any gas that escaped the system.

• Two liquid substances existed before and after they were mixed.

Answer explanation

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

A student trapped air inside a syringe (illustration A). She pushed the plunger down (illustration B) and then pulled the plunger up (illustration C). The dots represent the air particles. What happens to particles when you push the plunger down (B)?

• The air particles move closer together.

• The air particles move farther apart.

• There are more air particles in the syringe.

• There are fewer air particles in the syringe.

Tags

NGSS.MS-PS1-4

A jeweler heats a silver strip and bends it into a bracelet. When the strip of silver is heated, the silver particles _____.

• increase in number

• stop moving

• move faster and further apart

• get closer together and move more slowly

Answer explanation

This is a states of matter question. When you increase the temperature, the particle movement (kinetic energy) increases and they move further apart.

Tags

NGSS.MS-PS1-4

The iron cube and water in this system are at the same temperature. Which particles have higher average kinetic energy?

• The water particles

• The iron particles

• they both have the same kinetic energy

Answer explanation

By definition, temperature represents kinetic energy. Same temp = same kinetic energy

Tags

NGSS.MS-PS1-4

A student pours cold milk into a mug filled with hot chocolate. What 2 statements are true? *Law of thermodynamics

• Energy flows from the cold milk to the hot chocolate.

• Energy flows from the hot chocolate to the cold milk.

• The kinetic energy of the milk particles increases after it mixes with the hot chocolate

• The kinetic energy of the hot chocolate particles increases.

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-4

NGSS.MS-PS3-5

A baker has two identical cakes except that one cake is hot (40ºC), and the other cake is at room temperature (20ºC). He places both cakes next to each other on the same cold plate (10ºC). Which claim best explains what happens to the energy in the cakes?

• Only the hot cake transfers energy to the plate.

• The plate transfers energy to the room-temperature cake.

• Both cakes transfer energy to the plate.

• Neither cake transfers energy to the plate.

Answer explanation

Law of thermodynamics - heat moves. Both cakes are hotter than the plate, so both cakes transfer energy to the plate.

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-4

NGSS.MS-PS3-5