Stoichiometry

What is the formula for calculating number of moles of atoms?

• 3

• 6

• 4.5

• 9

• 2

• 3

• 4

• 5

Tags

NGSS.HS-PS1-7

A fixed mass of gas has a certain volume at a temperature of 50 °C. What temperature is required to double its volume while keeping the pressure constant?

• 100 K

• 323 K

• 373 K

• 646 K

Answer explanation

This is based on the ideal gas equations where PV/T is the same between 2 ideal gases.

Don't forget that T has to be converted to Kelvin first! So if we double volume, the temperature also has to double from 50C (which is 323 K), to 646 K.

Finish this statement of Avogadro's Law:

Equal volumes of all gases, when measured at the same temperature and pressure, ...

• ...have the same number of particles.

• ...will react at equal rates.

• ...will have the same mass.

• ...have the same density.

The graph represents the relationship between two variables in a fixed amount of gas.

Which variables could be represented by each axis?

• x: pressure

  y: temperature

• x: volume

  y: temperature

• x: pressure

  y: volume

• x: temperature

  y: volume

Answer explanation

While temperature does decrease with increasing volume, it is actually a linear relationship, not an inverse curve as shown.

A hydrocarbon contains 90% by mass of carbon. What is its empirical formula?

Answer explanation

Use the molar mass of each atom.

C3 = 12 x 3 = 36

H4 = 4 x 1 = 4

Percentage mass of carbon = 36/(36+4) = 36/40 = 0.9

Answer explanation

To convert 10 cm3 to dm3, divide by 1000 first. Then use the concentration equation:

c=n/v

or

n = cv

Tags

NGSS.HS-PS1-7