• 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)
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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