You should open the valve slowly in order to gradually vent excess pressure is an example of an effectively worded imperative mood step in a set of instructions.

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sodium i think the chemical element of atomic number 11, a soft silver-white reactive metal of the alkali metal group.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.