Methane $\left(\mathrm{CH}_4\right)$ is a gas.

(a) What is the ratio of carbon to hydrogen atoms?

(b) If a methane sample contains 1575 atoms, how many carbon and hydrogen atoms are present? Show your working:

(c) Can a sample of methane contain 1577 atoms? Explain your answer:

The enthalpy change for the reaction of hydrogen gas with fluorine gas to produce hydrogen fluoride is $-542 \mathrm{~kJ}$ for the equation as written:

$$\mathrm{H}_2(g)+\mathrm{F}_2(g) \rightarrow 2 \mathrm{HF}(g) \Delta H=-542 \mathrm{~kJ}$$

b. Is the reaction exothermic or endothermic as written?

Give the number of atoms of the specified element in a formula unit of each of the following compounds, and calculate the molecular (formula) mass:
(a) Oxygen in aluminum sulfate, $Al_2(SO_4)_3$
(b) Hydrogen in ammonium hydrogen phosphate, $(NH_4)_2HPO_4$
(c) Oxygen in the mineral azurite, $Cu_3(OH)_2(CO_3)_2$

Which of the following has more atoms: 0.302 g of hydrogen atoms or 14.7 g of chromium atoms?

A gaseous compound containing hydrogen and carbon is decomposed and found to contain $82.66 \%$ carbon and $17.34 \%$ hydrogen by mass. The mass of $158 \mathrm{~mL}$ of the gas, measured at $556 \mathrm{~mm} \mathrm{Hg}$ and $25^{\circ} \mathrm{C}$, is $0.275 \mathrm{~g}$. What is the molecular formula of the compound?

The red line in the spectrum of hydrogen has a wavelength of $656.3 \mathrm{~nm}$; the blue violet line in this spectrum has a wavelength of $434.2 \mathrm{~nm}$. If hydrogen light falls on a grating of $6000$ slits per centimeter, what will be the angular separation (in degrees) of these two spectral lines as seen in the firstorder spectrum?

Write the formulas for the following compounds: (a) rubidium nitrite, (b) potassium sulfide, (c) sodium hydrogen sulfide, (d) magnesium phosphate, (e) calcium hydrogen phosphate, (f) lead(II) carbonate, (g) tin(II) fluoride, (h) ammonium sulfate, (i) silver perchlorate, (j) boron trichloride

The mass of an electron is $9.1 \times 10^{-31} \mathrm{kg}$. The mass of a proton is $1.7 \times 10^{-27} \mathrm{kg}$. An electron and a proton are about $0.59 \times 10^{-10} \mathrm{m}$ apart in a hydrogen atom. What gravitational force exists between the proton and the electron of a hydrogen atom?

Chlorine has two natural isotopes: $^{37}_{17} \mathrm{Cl}$ and $^{35}_{17} \mathrm{Cl}.$ Hydrogen reacts with chlorine to form the compound HCl. Would a given amount of hydrogen react with different masses of the two chlorine isotopes? Does this conflict with the law of definite proportion? Why or why not?

A mixture of hydrogen and oxygen has a hydrogen mass fraction of 0.33. Determine the difference in the entropy of the mixture between a state of 750 kPa, $150^{\circ} \mathrm{C}$ and another state of $150\ \mathrm{kPa}, 150^{\circ} \mathrm{C},$ in $\mathrm{kJ}/ \mathrm{kg} \cdot \mathrm{K}.$

Write a general expression

$$a_n$$

in terms of n for finding the number of hydrogen atoms in an alkane molecule with n carbon atoms.

Chlorine has two natural isotopes: $^ {37} _ {17} \mathrm {Cl}$ and $^ {35} _ {17} \mathrm {Cl}.$ Hydrogen reacts with chlorine to form the compound HCl. Would a given amount of hydrogen react with different masses of the two chlorine isotopes? Does this conflict with the law of definite proportion? Why or why not?

Determine the temperature, in $\mathrm{K}$, at which $9 \%$ of diatomic hydrogen $\left(\mathrm{H}_2\right)$ dissociates into monatomic hydrogen ( $\left.\mathrm{H}\right)$ at a pressure of $10 \mathrm{~atm}$. For a greater percentage of $\mathrm{H}_2$ at the same pressure, would the temperature be higher or lower? Explain.

Butane is an unbranched alkane with the molecular formula $\ce{C4H10}$. Draw the complete structure of butane, including the hydrogen atoms.