Week 5 Application Exercises

1)

a)Exothermic. The burning of charcoal briquette releases heat during the process.
b) Endothermic – Water absorb the heat energy to evaporate.
c) Endothermic – Ice absorb the heat energy require to melt.

 

2)

ΔHoreaction=ΔHof(products)ΔHof(Reactants)

ΔHrxn=ΣΔHbreaking+ΣΔHmakingΔHrxn=ΣBEreactants−ΣBEproducts

Ans: A good explosion would have a very negative enthalpy, which means that the  bond strengths in reactants must be higher than products as you can see from the equation above.

 

3)

Heat is a form of energy transferred from one body to another, from a region of higher temperature to a region of lower temperature.

Temperature is not energy. It is a measure of the degree of hotness or coldness which is measured by different kinds of thermometer.

Q = mcΔT

Q = heat content in Joules

m = mass

c = specific heat, J/g °C

T = temperature

ΔT = change in temperature

Two different substances may have the same temperature but contains different amount of heat as the amount of heat depends on other factors such as mass and specific heat. Hence when a drop of hot water drops on you, you do not feel as pain as compared to a cup of hot water dropping on you as the cup of hot water contains higher mass which result in more heat being transferred to you.

 

 

4)

a) The knocking characteristics of this gasoline is 98% isooctane and 2% heptane.

b) The octane number of the gasoline does not tell us whether or not it contains oxygenates. But,we do know that fuel with oxygenates have higher octane ratings, with common oxygenated fuel additives having octane ratings of over 100.