Thermochemistry

• Heat is Thermal Energy which is transferred due to a difference in Temperature.

• Heat is transferred from higher temperature to lower temperature.

• Heat is transferred by collissions between ​molecules. At higher temperature, molecules have more Kinetic Energy (as they move faster), these collide with molecules with lower Energy thereby transferring this energy.

• Units are Joules (J) or Calories (cal)​

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• Temperature is the average Kinetic Energy of molecules within a system.

• Difference in Temperature causes Heat to Flow.​

• Can be measured using a Thermometer.

• Units - C, F, K, R

• K = C+273​

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• Heat EXITS the system or flows out.

• ​Given a negative sign. Imaging Money flowing out of your account which is bad and hence negative.

• This heat goes to the surroundings, which feel war​mer.

• ​As heat leaves the system, molecules SLOW DOWN.

• Gas > Liquid​ > Solid is example of Exothermic Process as Molecules are slowing down.

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• Heat ENDERS the system or flows in.

• ​Given a positive sign. Imaging Money flowing in your account which is good, will increase your balance and hence positive.

• This heat enters from surroundings, which feel colder.

• ​As heat enters the system, molecules SPEED UP.

• Solid > Liquid > Gas is example of Endothermic Process as Molecules are speeding up.

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• ​Start with Ice (SOLID) and heat it.

• Ice will rise in Temp till it reaches 0C.

• It will then melt to water (LIQUID). Temp does not change.

• Water(LIQUID) will then heat up as more heat is added.

• Water(LIQUID) will rise in Temp to 100C

• At 100C, ​Water changes to Steam.(GAS)

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Slope Part: (Red)

Temp increases as Heat is added.

​

Q = m x c x Δ​T

Q = Heat (J)

m = mass (g)

c = Specific Heat (J/gC)

​Δ​T = Change in Temp (Tf-Ti)

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Flat Part: (Blue)

Temp remains same as Heat is added.

All Heat is going towards Phase Change, called latent (lost) heat.

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Q = m x Δ​H

Q = Heat (J)

m = mass (g)

​Δ​H = Latent Heat (J/g)