We present a new set of analytic models for the expansion of H ii regions powered by ultraviolet (UV) photoionization from massive stars and compare them to a new suite of radiative magnetohydrodynamic simulations of turbulent, self-gravitating molecular clouds. To perform these simulations, we use ramses-rt, a Eulerian adaptive mesh magnetohydrodynamics code with radiative transfer of UV photons. Our analytic models successfully predict the global behaviour of the H ii region provided the density and velocity structure of the cloud are known. We give estimates for the H ii region behaviour based on a power-law fit to the density field assuming that the system is virialized. We give a radius at which the ionization front should stop expanding (‘stall’). If this radius is smaller than the distance to the edge of the cloud, the H ii region will be trapped by the cloud. This effect is more severe in collapsing clouds than in virialized clouds, since the density in the former increases dramatically over time, with much larger photon emission rates needed for the H ii region to escape a collapsing cloud. We also measure the response of Jeans unstable gas to the H ii regions to predict the impact of UV radiation on star formation in the cloud. We find that the mass in unstable gas can be explained by a model in which the clouds are evaporated by UV photons, suggesting that the net feedback on star formation should be negative.