Quantifying HeatThe Math!

Equation q = mCΔT

heat energy – measured in joules (J)

mass - measured in grams (g)

heat capacity – how much heat a substance can hold, measured in joules/gramdegrees Celsius

change in temperature, measured in °C ΔT = Tfinal – Tinitial

Units for heat (q)Most food tells us the amount of energy in

units of Calories. . . .

Calories are kilocalories (1 Cal = 1000cal)The SI unit for energy is Joules (J)1 cal = 4.184 J

Let’s do some quick conversions.

How can you tell if a process is endothermic or exothermic?

Endothermic q is a positive number

Why? The final temperature is

higher than the initial temperature- we added heat to the system.

ΔT = Tfinal – Tinitial

Exothermic q is a negative number

Why? The final temperature is

lower than the initial temperature- heat was given off from the system.

ΔT = Tfinal – Tinitial

Let’s solve some problems!