HW # 7: Heat and Its Measurement TEST: Thursday (10/20/16) HW # 7: Heat and Its Measurement

Aim 7 : How can we calculate the amount of heat to cause a temperature change?

DEMO A PAPER CUP BUNSEN BURNER

What is sublimation? Solid to Gas CO2 (s) CO2 (g)

Is an endothermic or exothermic reaction? Solid to Gas I2 (s) I2 (g)

Heating Curve for Water q =mHv q=mC∆T D E 100 ºC q=mC∆T 50 ºC q =mHf C B 0 ºC q=mC∆T - 10 ºC A HEAT ADDED

1. Heat Heat is energy Some reactions absorb energy (heat) and some give off energy (heat).

Energy is measured in joules. 2. Units of Energy Energy is measured in joules. 1 kilojoule = 1000 joules 1. Convert 40 Kj to joules 40 Kj x 1000 Joules Kj = 40 000 Joules

A bomb calorimeter A Bomb Calorimeter

A foam cup calorimeter here, two cups are nestled together for better insulation

So…how do we measure heat? We can only measure changes in heat (absolute heat doesn’t exist

3. Measurement of Heat The amount of heat absorbed or released in a reaction can be calculated using the following formulas: See table B and T

Solid, Liquid and Gas TABLE B q=mC∆T 4.18 _ J_ g K

Melting and Freezing TABLE B q =mHf 334 J g

Vaporization and Condensation TABLE B q =mHv 2260 J g

Table T: Heat q= mC∆T

q= mC∆T q= mC∆T q= mC∆T

4. How do you find ∆T? ∆T or temperature change ∆T = Tf - Ti Tf = final temperature Ti = initial temperature

Convert: 20 o C to Kelvin K = 20 + 273 K = 293 30 o C to Kelvin ∆T = Tf - Ti ∆T = 303 - 293 = 10

6. Heat of Fusion (Hf) Hf 334 J/g Amount of heat necessary to convert a given amount of a solid into a liquid. Hf 334 J/g MELTING B C FREEZING

334 J/g

Table T: Heat q= mHf

7. Heat of Vaporization 100 HV HV= 2,260 J/g Amount of heat necessary to vaporize a given amount of liquid at its boiling point. Boiling G Vaporization 100 Condensation L HV HV= 2,260 J/g

Table T: Heat q= mHv

HW # 7

1. How much energy in joules is absorbed by 30 grams of water when is heated from 20ºC to 30 ºC? DATA q= mC∆T Formula: q = X m = 30 g ∆T = 30ºC - 20ºC = 10ºC ∆T = 303 K - 293 K = 10 K 4.18 _J__ g ●K C = Table B

Using table T q = m C ∆T q = 30 g 4.18 J g ●K X X 10 K q = 1254 Joules

9. How many joules does it take to melt 35 g of ice at 0 ºC ? What do we mean by melt? Which formula are you going to use? Why ? HEAT OF FUSION: melting

Table T: Heat q= mHf

9. How many Joules does it take to melt 35 g of ice at 0 ºc? q = mHf q = 35 g X 334 Joules g q = 11690 Joules

8. How many joules are given off when 35 g of steam condense to liquid water? q = mHv q = ? m = 35 g Hv = 2260 Joules g

8. How many joules are given off when 35 g of steam condense to liquid water? q = mHv q = 35 g X 2260 Joules g q = 79000 Joules

Compare question 2 and 3 and write a conclusion!

The temperature of a 95. 4 g piece of copper increases from 25 The temperature of a 95.4 g piece of copper increases from 25.0 °C to 48.0 °C when the copper absorbs 849 J of heat. What is the specific heat of copper?

C= _ q___ m x ΔT C= 849 J 95.4 g x 23.0 °C

C= 0.387 J/g .°C

REVIEW ____ Solid to liquid ____ Liquid to gas ____ Gas to liquid ____ Liquid to solid ____ Solid to gas ____ Gas to solid Sublimation Boiling deposition Freezing Melting Condensation