Graham's Law Formula |
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\( \dfrac{ R_1 }{ R_2 } \;=\; \sqrt { \dfrac{ M_2 }{ M_1 } }\) (Graham's Law) \( R_1 \;=\; \dfrac{ R_2 \cdot \sqrt{ M_2 } }{ M_1 }\) \( R_2 \;=\; \dfrac{ R_1 \cdot M_1 }{ \sqrt{ M_2 } }\) \( M_2 \;=\; \dfrac{ R_1^2 \cdot M_1^2 }{ R_2^2 }\) \( M_1 \;=\; \dfrac{ R_2 \cdot \sqrt{ M_2 } }{ R_1 }\) |
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| Symbol | English | Metric |
| \( R_1 \) = Rate of Effusion Gas One (volume or number of moles per unit time) | \(mol\;/\;sec\) | \(mol\;/\;s\) |
| \( R_2 \) = Rate of Effusion Gas Two | \(mol\;/\;sec\) | \(mol\;/\;s\) |
| \( M_2 \) = Molar Mass Gas Two | \(lbm\;/\;mol\) | \(kg\;/\;mol\) |
| \( M_1 \) = Molar Mass Gas One | \(lbm\;/\;mol\) | \(kg\;/\;mol\) |
Graham's law, also called Graham's law of effusion, relates to the diffusion of gases. It states that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass, assuming other conditions such as temperature and pressure are constant. Or you could say the process in which one gas scatters itself within another. In simpler terms, lighter gases diffuse or effuse faster than heavier gases under the same conditions. This means that gases with lower molar masses will spread out more quickly and travel greater distances in a given amount of time compared to gases with higher molar masses.
This concept is particularly useful in understanding the behavior of gases and predicting their relative rates of diffusion or effusion. It has applications in various fields, including chemistry, physics, and atmospheric science.
