Unit 4 AP Chemistry

What is the final temperature of 15 g of nickel (C=0.44 J/g°C) that absorbs 240 J of energy at 15°C?

• 36°C

• -21°C

• 22°C

• 51°C

Answer explanation

Using Q=mCΔT, one finds the change of temperature to be 36°C. Add the initial temperature to find the final temperature of 51°C.

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NGSS.HS-PS3-1

NGSS.HS-PS3-4

Which of the following process is exothermic?

• CH4 (g) + 2O2(g) -> 2H2O(g) + CO2 (g)

• H2O (l) -> H2O (g)

• CO2 (s) -> CO2 (g)

• CaCO3 (s) -> CaO (s) + CO2(g)

Answer explanation

All combustion reactions are exothermic. Decomposition reactions are endothermic. Melting, evaporating, and sublimation are endothermic.

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

NGSS.HS-PS1-4

Which element is represented by this PES graph?

• argon

• potassium

• calcium

• scandium

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NGSS.HS-PS1-1

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The photoelectron spectra above show the energy required to remove a 1s electron from a nitrogen atom and from an oxygen atom. Which of the following statements best accounts for the peak in the upper spectrum being to the right of the peak in the lower spectrum?

• Nitrogen atoms have a half-filled p subshell.

• There are more electron-electron repulsions in oxygen atoms than in nitrogen atoms.

• Electrons in the p subshell of oxygen atoms provide more shielding than electrons in the p sub shell of nitrogen atoms.

• Nitrogen atoms have a smaller nuclear charge than oxygen atoms.

Answer explanation

"Nuclear charge" = charge of the nucleus. A greater nuclear charge will result in a greater attraction to the 1s electrons, and therefore more energy will be required to remove those electrons.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Which molecule would have this molecular geometry?

• BF₃

• CH₄

• PCl₅

• CO₂

How many sigma and pi bonds does this have?

• 1 sigma and 1 pi

• 2 sigma and 1 pi

• 1 sigma and 2 pi

• 2 sigma and 2 pi

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NGSS.HS-PS1-3

A sample of a hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became highly conductive when dissolved in water. Which of the following types of interactions is most likely found between the particles in the substance?

• Ionic bonds

• Metallic bonds

• Covalent bonds

• Hydrogen bonds

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NGSS.HS-PS1-3

Who could this be? 

• CO₂

• NH₃

• H₂S

• CH₄

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NGSS.HS-PS1-1

NGSS.HS-PS1-2

How many pi bonds does this have? 

• 1

• 2

• 3

• 4

Which substance would have the weakest intermolecular forces of attraction?

• CH₄

• NaCl

• H₂O

• MgF₂