Thermochemistry & Molar Mass

Limestone contains calcium carbonate (CaCO3)(CaCO3), which is reactive with hydrochloric acid (HCl). The graph shows that large chips of limestone take longer to react with a dilute solution of hydrochloric acid than the small limestone chips do. An investigation was performed with equal masses of different-sized chips.

• Larger chips have more impurities.

• Smaller chips are less concentrated.

• Smaller chips have a larger surface area.

• Larger chips have more calcium carbonate.

Tags

NGSS.HS-PS1-5

In an article, Felix reads about environmental contamination by a dangerous chemical called perchlorate. Scientists are working on a new catalyst to help decrease perchlorate in the environment. How would a catalyst help decrease perchlorate in the environment?

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• A catalyst would make perchlorate insoluble in water.

• A catalyst would separate perchlorate into separate elements.

• A catalyst would increase the rate that perchlorate reacts with other substances.

• A catalyst would bond with the perchlorate to make a new, harmless compound.

Tags

NGSS.HS-PS1-5

The rate at which a reaction occurs depends on the collisions between the molecules in the reactants. Which best describes the result of a temperature increase on the collisions of the molecules?

• The molecules are compressed, which decreases the number of collisions.

• The number of molecules increases, which increases the frequency of collisions.

• The molecules move faster, which increases the energy released by the collisions.

• The surface area of the molecules increases, which makes the collisions more effective.

Tags

NGSS.HS-PS1-5

Allyson and Cami add 25 mL of 3 M hydrochloric acid (HCl) to beakers containing 0 mL, 25 mL, 50 mL, and 75 mL of distilled water. The students then drop 5 cm of magnesium (Mg) ribbon into each beaker and measure the time for the magnesium to completely react with the acid. The results are shown in the data table.

Which statement best explains the change in reaction time as the amount of water increases?

• The magnesium remains separated from the acid.

• The concentration of the acid decreases.

• The volume of the mixture increases.

• The water is cooled by the acid.

Tags

NGSS.HS-PS1-5

Why is it necessary to keep fresh milk refrigerated instead of storing it on a kitchen counter?

• The chemical reactions that cause milk to spoil progress at a slower rate at lower temperatures.

• Milk tastes better when it is cold than when it is warm.

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    Milk will evaporate if it is not kept cold.

• Milk is a mixture, so the compounds that it is made of will separate at higher temperatures.

Tags

NGSS.HS-PS3-4

Which statement best describes the relationship between temperature and the rate of a chemical change?

• Increasing the temperature increases the energy of reactant particles, which causes more frequent collisions and a faster reaction rate.

• Increasing the temperature causes the reactant mixture to expand, decreasing the collision frequency and slowing the reaction rate.

• Increasing the temperature causes molecules to break apart and the reaction rate to slow to zero.

• Increasing the temperature does not affect the reaction rate because the particles move faster, but they are farther apart.

  Increasing the temperature does not affect the reaction rate because the particles move faster, but they are farther apart.

Tags

NGSS.HS-PS1-5

The reaction of calcium carbonate (CaCO3) and hydrochloric acid (HCl) produces carbon dioxide gas (CO2). A student places a block of CaCO3 into a beaker containing 100 mL HCl. Then the student mixes powdered CaCO3 into a second beaker containing 100 mL HCl. The second mixture bubbles rapidly, demonstrating a faster release of CO2 than in the first mixture. Which best explains the difference in observations?

• Powdered CaCO3 has a reduced boiling point

• Powdered CaCO3 can act as both a reactant and a catalyst.

• Powdered CaCO3 has weaker chemical bonds, increasing the reactivity.

• Powdered CaCO3 has a greater surface area, increasing the reaction rate.

Tags

NGSS.HS-PS1-5

Hydrogen peroxide (H2O2) naturally reacts to produce water (H2O) and oxygen (O2).

2H2O2→2H2O+O2

When manganese (IV)oxide (MnO2) is mixed with H2O2 the reaction rate increases and the same products are formed. What is the most likely function of MnO2 in this chemical reaction?

• reactant

• catalyst

• electron donor

• limiting reagent

Tags

NGSS.HS-PS1-5

Equal masses of steel wool are placed in four beakers. Equal amounts of hydrochloric acid (HCl) are added to three beakers in the following concentrations: 0.5 M, 1.0 M, and 3.0 M. Water is added to the fourth beaker. Hydrochloric acid reacts with the metal in steel wool. Which observation is most likely?

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    The steel wool in the 0.5 M HCl reacts fastest.

• The steel wool in the 3.0 M HCl reacts fastest.

• The mixtures react in the same amount of time.

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    The control reacts in the shortest amount of time.

Tags

NGSS.HS-PS1-5

Mark and Elizabeth are combining two substances, X and Y, in chemistry class. Substance X is a solid and Substance Y is a liquid. They are investigating the rate of reaction between the two substances. In a reaction between Substances X and Y, which action would most likely increase the reaction rate?

• adding more of X and Y

• lowering the temperature of Y

• using smaller sized particles of X

• increasing the pressure on X and Y

Tags

NGSS.HS-PS1-5