Biology: Energy Changes Essay

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Smith (Chapter 6)

6.1 Energy

Chapter 6:
Energy Changes,
Reaction Rates,
& Equilibrium

•Energy is the capacity to do work.

stored
•Potential energy is ________________ energy. motion •Kinetic energy is the energy of ________________.

6.1 Energy
6.2 Energy Changes in Reactions
6.3 Energy Diagrams
6.4 Reaction Rates
6.5 Equilibrium
6.6 Le Châtelier’s Principle
6.7 Focus on the Human Body: Body Temperature
Adapted from material Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

•The law of conservation of energy states that the

does not change total energy in a system ________________.
Energy cannot be created or destroyed.
2

1

6.1 Energy

6.1 Energy

A. The Units of Energy

bonds chemical •_____________ _____________ store potential energy. lower •A compound with ________________ potential energy is more stable than a compound with higher potential energy. •Reactions that form products having lower potential energy than the reactants are usually favored.

calorie
•A ________________ (cal) is the amount of energy needed to raise the temperature of 1 g of water by 1 oC. joule •A ________________ (J) is another unit of energy.
1 cal = 4.184 J
•Both joules and calories can be reported in the kilojoules larger units _______________________ (kJ) and kilocalories _______________________ (kcal).
1,000 J = 1 kJ

3

1,000 cal = 1 kcal

1 kcal = 4.184 kJ

4

1

Smith (Chapter 6)

6.2 Energy Changes in Reactions

6.2 Energy Changes in Reactions

A. Bond Dissociation Energy

•When molecules come together and react, bonds are broken in the reactants and new bonds are formed in the products.

• delta H the energy absorbed or released in is a reaction; it is called the heat of reaction or enthalpy the _______________________ change.

input of
•Bond breaking always requires an _____________ energy _________________________________.

absorbed
•When energy is ______________, the reaction is said to be endothermic and H is positive (+).

will be release of energy
•Bond formation always __________________________.
To cleave this bond,
58 kcal/mol must be added ________________.

Cl

Cl

To form this bond,
58 kcal/mol is
5
released
_________________.

released
•When energy is _______________, the reaction is said to be exothermic and H is negative ( ).
To cleave this bond,
+58
H = ______kcal/mol.

6.2 Energy Changes in Reactions

dissociation energy.

always +
•BDEs are ____________ values, because bond breaking is endothermic ( H > 0).
H +

H

•Bond formation always has negative values, exothermic because bond formation is _________________ ( H < 0).
H

+

H

H

H

delta H= 104 Kcal/mole

To form this bond,
6
-58
H = _______kcal/mol.

A. Bond Dissociation Energy higher/greater •The stronger the bond, the _____________ its bond

dissociation
•The bond _______________ energy (BDE) is the H for breaking a covalent bond by equally dividing the e between the two atoms.

H

Cl

6.2 Energy Changes in Reactions

A. Bond Dissociation Energy

H

Cl

7

•In comparing bonds formed from elements in the same group, bond dissociation energies generally decrease ______________________ going down the column.

High BDE = strongest bond H =

+136

_______ kcal/mole +103
_______
kcal/mole

low BED= weakest bond +88
_______
kcal/mole

+71 8
_______
kcal/mole

2

Smith (Chapter 6)

6.2 Energy Changes in Reactions

6.2 Energy Changes in Reactions

B. Calculations Involving H Values relative strength
H indicates the _______________________of the bonds broken and formed in a reaction.

When H is positive:
•More energy is needed to break bonds than is released in the formation of new bonds.

When H is negative:
•More energy is released in forming bonds than is needed to break the bonds.
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