Temperature

(“Degree of hotness”) - is the distribution of energy through the molecules. - related to the motion (speed) of molecules.

Heat ≠ Temperature Heat (“Quantity of hotness”) - is a form of energy. [units: Joules (J)] - related to both the motion and mass of molecules.

q = m x ∆T x c Heat = mass x ∆T x C p

J g o C J/g o C

Specific heat (C p

) = amount of heat energy required to raise 1 g of a substance 1 o C.

Specific heat for water = 4.18 J/g

o C

Thermal calories 1 cal = 4.18 J vs.

Food Calories 1 Cal = 1000 calories = 1 kcal

Practice

Calculate the quantity of energy needed to heat 8.0 g of water from 42.0 o C to 45.0 o C.

Heat = mass x



T x spec. heat

(45.0 - 42.0) ? J = 8.0 g x 3.0

 C x 4.18 J/g  C = 1.0 x 10

2 J

(100.32)

Practice

A 110.0-g sample of iron at 55.5 o C raises the temperature of 150.0 mL of water from 23.0 o C to 25.5 o C. Determine the specific heat of the iron in J/g o C.

Heat = mass x



T x spec. heat

Heat gain (H 2 O) = heat loss (metal) Heat = 150.0 g x 2.5

 C x 4.18 J/g  C (gained by H 2 O) ( 25.5- 23.0) = 1567.5 J (2 sigs) 1600 J

Heat gained by H 2 O = 1567.5 J (2 sigs) 1600 J = heat lost by metal

Heat = mass x



T x spec. heat

Heat lost by metal: 1600 J = 110.0 g x 30.0

 C x spec.heat

(55.5 – 25.5) Spec.heat (C p ) = 0.48 J/g

o C

Read Sect 15.1 pgs 516-522 Do Problems: 1 & 2, pg 519 4, 5, 6 pg 521 Read Sect 15.2 pgs 523-528 Do Problems: 12 - 15, pg 525