Specific Heat Capacity

ANNOUNCEMENTS

• Unit 9 test tomorrow!

Take 1

Things heat/cool at different rates

• Everything changes temperature when it is heated or cooled, but certain things change temperature faster/slower than others.

• For example, put a metal skillet on a stove and it heats up quickly, so fast that it can burn you.

• Put water in a skillet on the stove, and the metal skillet heats faster than the water.

Why?

• Water is more resistant to a change in temperature than metal.

• In other words, water has a higher heat capacity.

• Heat capacity- The quantity of heat energy to change the temperature of a substance by 1°C.

• Every different element has a specific heat capacity.

Some heat capacities Substance Specific Heat Capacity

Lead .128 J/g °C

Gold .128 J/g °C

Silver .235 J/g °C

Copper .385 J/g °C

Iron .449 J/g °C

Aluminum .903 J/g °C

Water 4.18 J/g °C

Do you notice a difference in heat capacity between water and the metals?

So?

• Water has a much higher heat capacity than the metals in the table.

• What does that mean? (Review of the definition of heat capacity)

Water takes more energy to heat 1 °C than the metals.

Apply

• If water has a higher specific heat capacity than the metals that make up the soil and rocks around us, why might a city by the water have lower temperature than a city that is surrounded by land?

Solving problems with heat capacity

• Often in chemistry we want to know how much heat must be absorbed or lost in order for a compound to change temperatures.

• This is why we have an easy formula to find heat gained and heat lost.

Formula

• q= m*C*ΔT• q=heat • m= mass of substance• C= specific heat capacity • ΔT=change in temperature

• SIDENOTE: Δ means change in any situation

Problem

• q=mCΔT• How much heat must be absorbed for 2

grams of copper to heat from 25 °C to 1084 °C? The specific heat of copper is .385 J/g °C.

• q=• m=• C=• ΔT=

?3g

.3851084-25=1059 °C

Solved

• q=m x C x ΔT

• ?=(3) x (.385) x (1059) =

• In other words, it takes 1223.14 Joules of energy to heat copper 1059 °C

1223.14

Guided

• Now lets work a few more problems on the board together.

• Next- Practice work to really get it down.

Remastery time!

Last minutes

• What did we learn?

• Top ten: how’d we do?