Unit 2 – Matter and Energy Mrs. Callender

Lesson Essential Question: What is Thermochemistry?

Thermochemistry is the study of the motion of heat energy as it is transferred from the system to the surrounding or from the surrounding to the system.

Heat Symbolized by symbol q When heat is lost - exothermic q is negative (-q).

Heat Symbolized by symbol q When heat is gained - endothermic q is positive (+q).

Converting Between Celsius and Kelvin Temperature K = o C Or o C = K - 273

Convert the Following To Kelvin o C o C o C o C To Celsius K K K4. 0 K 306 K 248 K 283 K 773 K -373 o C-263 o C -273 o C 250 o C

Specific Heat - Cp The quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius (or one Kelvin). J/gK or J/g o C Cp of water is J/gK or J/g o C

To Calculate Heat q = mCp Δ T q = heat in Joules (J) m = mass in Grams (g) Cp = specific heat in J/g o C or J/gK Δ T = Change in Temperature o C or K

Example problem #1 A 4.0 g sample of glass was heated from 274 K to 314 K and was found to absorb 32 J of energy as heat. Calculate the specific heat of this glass. q = mCp Δ T 32 J = (314 K – 274 K) (4.0 g) Cp 32 J (4.0 g) = Cp (40K) 32 J = (160 g K) Cp (160 g K) Cp = (0.20 J/g K)

Example problem #2 If 980 kJ of energy as heat are transferred to 6.2L of water at 291 K, what will the final temperature of the water be? The specific heat of water is 4.18 J/g K q = mCp Δ T 980,000J = (T f – 291 K) (6,200 g) (4.184 J/gK) 980,000 J (25941 ) = 980,000 J = 25941T f - 7,548, ,528,772 = 328 K (T f – 291 K) +7,548, T f = = T f