How is enthalpy used to predict whether a reaction is endothermic or exothermic?
are ch4 (g): hf = –74.6 kj/mol; co2 (g): hf = –393.5 kj/mol; and h2 o(g): hf = –241.82 kj/mol.
how much heat is released by the combustion of 2 mol of methane?

heat is released by the combustion of of methane

Explanation:

The value of enthalpy determines whether the reaction is exothermic or endothermic. If the enthalpy change is positive, then the reaction is endothermic (heat or energy released) and if the enthalpy change is negative then the reaction is exothermic (heat or energy absorbed).

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In this question, the enthalpy of formation has positive value and hence the reaction is endothermic in which the heat is released.

stratosphere: as the altitude increases, the air temperature increases. the stratosphere has a layer of ozone, called the ozone layer. this layer absorbs most of the ultraviolet radiation from sunlight. this results in the stratosphere being warmer.

i would have a lunch. it's one big package of food, making it one food. : p