# Which statement represents the second law of thermodynamics?

A, B and C are opposite 2nd law D does not violate the 2nd law, Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature. Informally, “Heat doesn’t flow from cold to hot (without work input)”, which is true obviously from ordinary experience. For example in a refrigerator, heat flows from cold to hot, but only when aided by an external agent (i.e. the compressor). Note that from the mathematical definition of entropy, a process in which heat flows from cold to hot has decreasing entropy. This can happen in a non-isolated system if entropy is created elsewhere, such that the total entropy is constant or increasing, as required by the second law. For example, the electrical energy going into a refrigerator is converted to heat and goes out the back, representing a net increase in entropy.