Chemistry Week 29

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Chemistry Week 29. Please get out your notebooks and homework!. April 4, 2012. AGENDA: 1 – Bell Ringer &amp; Agenda 2 – Examples: How to calculate heat when temperature is changing and constant 3 – Review Homework 4 – Work Time: More Heat Calculations. Today’s Goal:

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Chemistry Week 29

notebooks and homework!

April 4, 2012

AGENDA:

1 – Bell Ringer & Agenda

2– Examples: How to calculate heat when temperature is changing and constant

3 – Review Homework

4 – Work Time: More Heat Calculations

Today’s Goal:

Students will be able to solve heat calculations when temperature is changing and when temperature is constant.

Homework

• More Heat Calculations
• Binder Check!
Thursday, April 4th

Objective:

Students will be able to solve heat calculations when temperature is changing and when temperature is constant.

Bell Ringer: If a bag of Flamin Hot Cheetos has 170 Calories, how many Joules of energy are you consuming if you eat a bag?

(*Remember 1 Calorie = 4184 J)

Thursday, April 4th

Objective:

Students will be able to solve heat calculations when temperature is changing and when temperature is constant.

Bell Ringer: If a bag of Flamin Hot Cheetos has 170 Calories, how many Joules of energy are you consuming if you eat a bag?

(*Remember 1 Calorie = 4184 J)

April 4, 2012

AGENDA:

1 – Bell Ringer & Agenda

2– Examples: How to calculate heat when temperature is changing and constant

3 – Review Homework

4 – Work Time: More Heat Calculations

Today’s Goal:

Students will be able to solve heat calculations when temperature is changing and when temperature is constant.

Homework

• More Heat Calculations
• Binder Check!
Cornell Notes
• Topic:Review Heat Calculations
• Date:4/4/2013

Heat Capacity = the amount of heat required to change the temperature of an object (based on the specific heat).

q = m · Cp · ∆T  Units = J = g· (J/g°C) · °C

Molar Heat of Fusion (HF): the heat absorbed by one mole of a solid substance as it melts or freezes at constant temperature.

q = HF · m  Units: J = (J/g) · g

Molar Heat of Vaporization (HV): the heat necessary to vaporize or condense one mole of a substance at constant temperature.

q = HV· m  Units: J = (J/g) · g

What is heat capacity?

What is the heat of fusion?

What is the heat of vaporization?

Cornell Notes

Use this equation to calculate the heat released (q = neg.) or absorbed (q = pos.) when temperature is changing.

q = m · Cp · ∆T

Use this equation if you are calculating the heat released (q = neg.) or absorbed (q = pos.) when substance is melting or freezing.

q = HF · m

Use this equation if you are calculating the heat released (q = neg.) or absorbed (q = pos.) when substance is boiling (evaporating) or condensing.

q = HV· m

When to use heat capacity:

When to use heat of fusion:

When to use heat of vaporization:

Cornell Notes

How much heat does 10 g of water absorb if it is heated from 10°C to 25°C? q = m · Cp · ∆T

q = (10 g) ·(4.184 J/g°C)·(25 °C - 10°C) = 627.6 J

How much heat is released when 10 grams of water melts?q = HF · m

q = (334 J/g)·(10g) = - 3340 J

How much heat is absorbed if 5 grams of water evaporates (boils)? q = HV· m

q = (2260 J/g)·(60g) = 11,300 J

Calculating using heat capacity:

Calculatingusing heat of fusion:

Calculating using heat of vaporization:

Cornell Notes

Diagram Heat Curves.

Endothermic = system

Vapor/Gas

Boiling

To calculate heat, temperature is not changing so you would use q = HV·m

Liquid

Melting

To calculate heat, temperature is changing so you would use q = m·CP·∆T

Solid

Cornell Notes

Diagram Heat Curves.

Exothermic = system

Vapor/Gas

*Remember the sign of q will be opposite!

Condensing

Liquid

To calculate heat, temperature is not changing so you would use q = HF·m

To calculate heat, temperature is changing so you would use

q = m·CP·∆T

Freezing

Solid

More Practice Problems (Show work on loose leaf paper)

1. What is the amount of energy need to vaporize 3500 g of water?

2. Calculate the amount of energy needed to melt 10 grams of mercury.

3. What is the amount of energy needed to vaporize 360 grams of butane.

4. What is the amount of energy released when 15 g of ether freezes.

5. Challenge:How many joules of energy are absorbed when 25g of steam cools from 100oC to produce water at 10oC? (2-step)