We’re being asked to **determine the normal boiling point** of ammonia. We’re given the vapor pressure at different temperatures.

For this problem, we can use the ** Clausius-Clapeyron Equation**:

$\overline{){\mathbf{ln}}\frac{{\mathbf{P}}_{\mathbf{2}}}{{\mathbf{P}}_{\mathbf{1}}}{\mathbf{=}}{\mathbf{-}}\frac{{\mathbf{\Delta H}}_{\mathbf{vap}}}{\mathbf{R}}\left[\frac{\mathbf{1}}{{\mathbf{T}}_{\mathbf{2}}}\mathbf{-}\frac{\mathbf{1}}{{\mathbf{T}}_{\mathbf{1}}}\right]}$

where:

**P _{1}** = vapor pressure at T

**P _{2}** = vapor pressure at T

**ΔH _{vap}** = heat of vaporization (in J/mol)

**R** = gas constant (8.314 J/mol•K)

**T _{1} and T_{2}** = temperature (in K).

The vapor pressure of ammonia at several different temperatures is shown below.

Temperature (K) | Pressure (torr) |

200 | 65.3 |

210 | 134.3 |

220 | 255.7 |

230 | 456.0 |

235 | 597.0 |

Determine the normal boiling point of ammonia.

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What scientific concept do you need to know in order to solve this problem?

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