In gen chem, and any hard science lab, a major part of lab reports is including sources of systematic error. This past lab was focused around determining the equilibrium constant of several different solutions. One of the determining factors of whether or not equilibrium can be reached is that temperature must be held constant. In the lab, my seat just happens to be incredibly close to the huge-normous windows that are not suited for keeping students warm. Let the scene be set halfway through the lab, with a freezing small person like myself hard at work.
Me: "Andrew why is it so cold?"
Andrew: *heads towards the heaters under the windows*
Me: "they're not on, I checked"
Andrew: "well I'm sorry, there's nothing I can do"
(several minutes later)
Me: "Andrew, because chemical equilibrium can only be reached when the temperature is constant in the environment, isn't this entire lab invalid!?"
Andrew: "I guess that will be one of your sources of error..."