A cell at 25 °C is constructed as
Pt|H_{2}(g, P_{H2}= ? atm), H^{+}(aq, 0.0010 M)‖Cu^{2+}(aq, 1.00 M)|Cu(s)
The measured cell potential is 0.310 V, and the copper electrode is the cathode. The standard potential for the cell is 0.340 V. Determine the partial pressure of H_{2} gas required to generate the observed potential. Report P_{H2} in atmospheres to two significant figures.