Problem: Write a balanced equation and draw an enthalpy diagram for (select if exothermic or endothermic):combustion of one mole of methanevaporization of liquid alcoholfreezing of liquid waterformation of 1 mole of potassium chloride from its elements (heat is released)

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Exothermic reactions

▪ lose energy, releases heat, temperature of the surroundings increases
▪ involves bond formation (for phase change: gas → liquid → solid)
▪ ΔH is negative

Endothermic reactions

▪ gain/requires energy, absorbs heat, temperature of the surroundings decreases
▪ involves breaking bonds (for phase change: solid → liquid → gas)
▪ ΔH is positive


• combustion of one mole of methane

Reaction:      CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)

▪ releases heat:   exothermic



• vaporization of liquid alcohol 

*generic form of alcohol: R‒OH

Reaction:      R‒OH(l) → R‒OH(g)

▪ phase change (liquid → gas):    endothermic



• freezing of liquid water

Reaction:      H2O(l) → H2O(s)

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Problem Details

Write a balanced equation and draw an enthalpy diagram for (select if exothermic or endothermic):

combustion of one mole of methane

vaporization of liquid alcohol

freezing of liquid water

formation of 1 mole of potassium chloride from its elements (heat is released)

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