C. Use the equation C(s) + 2H2(g) CH4(g), ΔH = –74.85, for the following questions. (5 points)
i. Is the formation of methane (CH4) an exothermic or endothermic reaction? (1 point)

ii. Draw a potential energy diagram for the reaction. (2 points)

iii. Label the graph with the following: "Reactants," "Products," "ΔHreaction," and "Ea." (2 points)

frequency, z, and the collision density, z, in carbon dioxide (co2), r 180 pm at 30 °c and 120 kpa

the answer is 75.0%.

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.