Question

When formic acid is heated, it decomposes to hydrogen and carbon dioxide in a first-order decay: . . HCOOH(g) →CO2(g) + H2 (g) . . The rate of reaction is monitored by measuring the total pressure in the reaction container. . . Time (s) . . . P (torr) . 0 . . . . . . . . . 220 . 50 . . . . . . . . 324 . 100 . . . . . . . 379 . 150 . . . . . . . 408 . 200 . . . . . . . 423 . 250 . . . . . . . 431 . 300 . . . . . . . 435 . . At the start of the reaction (time = 0), only formic acid is present. What is the formic acid pressure (in torr) when the total pressure is 291? half-life in sec? What is the rate constant (in s-1)?

Answer 1

We are given with the reaction HCOOH(g) →CO2(g) + H2 (g). According to Dalton's law, the total pressure of a vessel is equal to the sum of the partial pressure of the components inside it. In this case, we plot first the data ln (ratio partial pressure of HCOOH to total pressure) vs time. Partial pressure is the difference of pressure (from one point to another). In this case, the equation is ln P(HCCOH) = -0.0146t - 0.2281 where R² = 0.9923. K is equal to  -0.0146 s-1. When the total pressure is 291, ln P is -0.66938, thus the time is 30.23 seconds. The half life is ln(0.5)/k equal to 47.46 seconds.