Attili Chemical and Physical Changes Review

Bella mixes salt and water to make saltwater, then heats the saltwater until the water evaporates, leaving salt behind. They also toast bread in a toaster. Which statement best describes the types of changes that occurred when making the saltwater and toasting the bread?

• Both the saltwater and the toasted bread are formed by physical changes.

• Both the saltwater and the toasted bread are formed by chemical changes.

• The saltwater is formed by a physical change, and the toasted bread is formed by a chemical change.

• The toasted bread is formed by a physical change, and the saltwater is formed by a chemical change.

Answer explanation

The saltwater is created by dissolving salt in water, a physical change. When toasting bread, chemical reactions occur, changing its composition and flavor, making it a chemical change. Thus, the correct statement is that the saltwater is a physical change, and the toasted bread is a chemical change.

Abby is baking a cake. She notices that as the cake bakes, it changes color and releases a pleasant odor. Which of the following best describes what is happening?

• The color change is a sign of a physical change and the odor is a sign of a chemical change

• Only the substance's physical properties are being changed.

• The smell and color change are examples of a chemical change.

• None of the substances change in the composition

Answer explanation

The smell and color change indicate that chemical reactions are occurring as the cake bakes, transforming the ingredients and creating new substances, which is characteristic of a chemical change.

Tags

NGSS.MS-PS1-2

Yander heats water in a test tube over a small flame. Which scenario would best demonstrate the Law of Conservation of Mass?

• Open test tube held with tongs over a flame.

• Test tube with a balloon attached over the opening, heated over a flame.

• Flame turned off after heating test tube for five minutes.

• Test tube submerged in water after heating over flame.

Answer explanation

The test tube with a balloon attached captures any gas produced during heating, demonstrating that mass is conserved. In contrast, the open test tube allows gas to escape, violating the Law of Conservation of Mass.

Tags

NGSS.MS-PS1-5

Mirian heats a sample of sodium bicarbonate (NaHCO3) in a test tube. After heating, the mass of the solid decreases. Which statement best explains the decrease in mass?

• Some of the mass escaped as vapor during heating.

• The lost mass was destroyed in the reaction.

• Mass is not conserved when gases are produced.

• Some sodium bicarbonate melted and was destroyed.

Answer explanation

The decrease in mass is due to some of the sodium bicarbonate decomposing into gases, which escape as vapor during heating. This explains why the mass of the solid decreases.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

Allan combined hydrogen peroxide and yeast in a closed flask. According to the Law of Conservation of Mass, which statement best describes what happens during this chemical reaction?

• Atoms are lost during the reaction, causing a decrease in mass.

• New atoms are created, resulting in an increase in mass.

• New substances are produced, but the total mass remains unchanged.

• The mass of the products is less than the mass of the reactants.

Answer explanation

According to the Law of Conservation of Mass, during the reaction between hydrogen peroxide and yeast, new substances are formed, but the total mass of the reactants and products remains unchanged.

Tags

NGSS.MS-PS1-5

During a classroom experiment, Remmier and Tyron mix hydrogen peroxide with yeast to observe a chemical reaction. If they want the reaction to happen faster without changing the substances produced, what should they do?

• Use more yeast.

• Cool the mixture with ice.

• Heat the mixture.

• Add water to dilute the hydrogen peroxide.

Answer explanation

Heating the mixture gently increases the kinetic energy of the molecules, leading to more frequent and effective collisions between the yeast and hydrogen peroxide, thus speeding up the reaction without altering the products.

Tags

NGSS.MS-PS3-4

NGSS.MS-PS3-3

Christofer and Keyler activate two glow sticks at the same time. They place one in ice water and the other in warm water. What is the most likely difference they will observe between the two glow sticks after a few minutes?

• The glow stick in ice water will not light up because the reaction cannot occur at low temperatures.

• The glow stick in warm water will be brighter than the one in ice water because the reaction happens faster at higher temperatures.

• The glow stick in ice water will change color while the one in warm water will not.

• Both glow sticks will have the same brightness regardless of temperature.

Answer explanation

The glow stick in warm water will be brighter because higher temperatures increase the reaction rate, leading to more light production. In contrast, the cold temperature slows down the reaction in the ice water glow stick.

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-4

Anna-Tae combines warm lemon juice with baking soda at room temperature and notices bubbling. If the lemon juice is cooled even further to 5°C before mixing with baking soda, how will the temperature most likely affect the rate of reaction?

• The rate of reaction would increase.

• The rate of reaction would decrease.

• The reaction would not occur.

• The temperature would have no effect.

Answer explanation

Cooling the lemon juice to 5°C decreases the kinetic energy of the molecules, leading to fewer collisions between reactants. This results in a slower reaction rate, making the correct choice "The rate of reaction would decrease."

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-4

Nevaeh and Naika set up four test tubes, each containing a zinc strip submerged in copper sulfate solution heated to different temperatures: Test Tube A = 15 °C, Test Tube B = 35 °C, Test Tube C = 55 °C, Test Tube D = 70 °C. Which option correctly identifies the dependent variable and the expected outcome based on temperature’s effect on reaction rate?

• Temperature of solution is the dependent variable; Test Tube A zinc strip would react the slowest because it is in the coldest solution.

• Temperature of solution is the dependent variable; Test Tube D zinc strip would react the slowest because it is in the warmest solution.

• Rate of reaction is the dependent variable; Test Tube A zinc strip would react the fastest because it is in the coldest solution.

• Rate of reaction is the dependent variable; Test Tube D zinc strip would react the fastest because it is in the warmest solution.

Answer explanation

The rate of reaction is the dependent variable, as it depends on temperature. Test Tube D, at 70 °C, will have the fastest reaction due to increased kinetic energy, while Test Tube A, at 15 °C, will react the slowest.

Deandre and Christopher were presented with three processes involving temperature increases: iron to rust (60 °F to 120 °F), batter to pancake (70 °F to 400 °F), and fruit juice to vinegar (65 °F to 95 °F). Which observation most directly supports the conclusion that chemical changes are often associated with rising temperatures?

• As the temperature increased, the substance underwent a noticeable, visible transformation.

• As the temperature decreased, the substance underwent a noticeable, visible transformation.

• As the temperature increased, the mass of the original substance decreased.

• As the temperature decreased, the volume of the original substance increased.

Answer explanation

The correct choice highlights that as temperature increased, a noticeable transformation occurred, indicating a chemical change. This supports the conclusion that rising temperatures are often linked to chemical changes.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-4

NGSS.MS-PS3-4