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### THERMOCHEMISTRY

Think-pair-share

- Respond to at least One question below using the organizer provided. Be prepared to share your thoughts
- QUESTIONS:
- 1. Describe what happens to a rat that has been eaten by a python.
- 2. What is the function of the digestive system? What are calories?
- 3.How can you measure the calories contained in food?
- 4. What do you think happens if a person eats more calories than their body needs?

http://ca.pbslearningmedia.org/resource/nvsn6.sci.bio.fuel/food-is-fuel/

SWBAT…..

- define the terms system and surroundings in the context of a chemical reaction.
- identify the system and surroundings in a thermochemicalreaction.
- describe how heat is transferred in endothermic and exothermic reactions
- Calculate specific heat of a substance in calories and joules
- Calculate enthalpy changes in a thermochemicalrtn
- Apply Hess’s law of heat summation in a thermochemical equation.

Heat and Work:

- TERMINOLOGIES:
- Thermochemistry: studies energy changes in chemical reactions and changes of state.
- Heat (q): is the transfer of energy from one object to another because of temperature difference (warmer to cooler object)
- System: part of the universe being studied or focus of attention (e.g. reactants and products of a reaction)
- Surroundings: the immediate vicinity of the system (e.g. container, space, universe, e.t.c.)
- Law of conservation of energy: states that energy is neither created nor destroyed in any chemical or physical process.

Exothermic and EndothermicProcesses

- COMPARE AND CONTRAST USING VENN DIAGRAM
- Exothermic Process:
- Heat is release to the surroundings (surroundings warms up)
- The system loses heat (system products cools down)
- q= negative

- Endothermic Process:
- Heat is absorbed from the surroundings (surroundings cool down)
- The system gains heat (system products warms up)
- q= positive

Unit for Measuring Heat Flow

- Calorie (cal) : quantity of heat needed to raise the temperature of 1g of pure water to 10C.
- 1 Calorie = 1 Kilocalorie = 1000 calories
- 20 Cal (dietary potential energy) = 20 Kcal (when energy completely used up/released)

- Joules (S.I. Unit of energy)
- One Joule (1J) of heat is the energy needed to raise the temperature of 1g of pure water to 0.23900C
- Unit Conversion:
- 1J = 0.2390 cal 4.184J = 1cal
- 1000J = 1kJ (kiloJoules)

Heat Capacity

- Heat Capacity: amount of heat needed to increase the temperature of an object to exactly 10C. ( Unit for heat capacity = J/0C)
- Heat capacity depends on:
- Mass of an object
- Chemical composition of the object

- Specific Heat Capacity (C): is the amount of heat it takes to raise the temperature of 1g of substance (object) to 10C. (Unit for Specific Heat = J/(g.0C) or J/(kg.0C) or kcal/(kg.0C) ). Remember: 1000g = 1Kg

Check for understanding

- Thumbs Up
- Thumbs Down
- Thumbs side
- What is your level of understanding on:
- System and surroundings
- Endothermic and Exothermic
- Calorie/Kilocalorie
- Heat Capacity
- Specific Heat Capacity

Calculating Specific Heat/Capacity(C) of a Substance

- Formula for calculating Specific Heat
- Unit for Specific Heat
- Specific Heats of some common substances (see PHC: table 17.1, page 508)

Heat Math problems

- When 435J of heat is added to 3.4g of olive oil at 210C, the temperature increases to 850C. What is the specific heat of the olive oil?
- How much heat is required to raise the temperature of 250.0g of mercury 520C?
- An orange contains 445kJ of energy. What mass of water could the same amount of energy raise from 25.00C to the boiling point?

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