Chemistry Unit 4 Lesson 2

Study Notes

Energy in Chemical Reactions

Chemical reactions are influenced by energy changes, prominently thermal energy.
Energy changes during reactions and phase transitions help predict reaction feasibility.
Topics include thermal energy, heat, enthalpy, specific heat, and thermodynamic laws.

Dynamite and Explosive Energy

Dynamite, invented by Alfred Nobel in 1866, releases significant heat and light energy upon explosion.
The explosion highlights the potential energy stored in chemical bonds of nitroglycerin (C3H5(NO3)3).
Chemical reactions can either release or absorb energy, a key element in chemical thermodynamics.

Energy and Mass in Reactions

Exothermic reactions release energy; endothermic reactions absorb energy.
Mass is conserved during chemical reactions, ensuring that reactants and products maintain total mass.

Chemical Reactions and Energy Dynamics

Nitroglycerin becomes explosive due to its unstable nature; mixing with diatomaceous earth allows safe handling.
The energy release during nitroglycerin decomposition is exemplified in the reaction yielding nitrogen, carbon dioxide, water, and oxygen.

Heat Transfer in Reactions

Exothermic reactions often result in an increase in surrounding temperature, while endothermic reactions lead to a decrease.
Combustion reactions are classic exothermic reactions due to heat release.

Changes of State

Mutual behavior of solids, liquids, and gases determines endothermic and exothermic nature.
Melting ice is endothermic, absorbing heat; freezing water is exothermic, releasing heat.

Everyday Examples of Reactions

Hand warmers operate through exothermic reactions involving iron powder oxidation, releasing heat when activated.
Instant heat packs and cold packs illustrate energy absorption and release through chemical interactions, respectively.

Laws of Energy and Mass

The total energy in any chemical reaction remains constant, adhering to the law of conservation of energy.
Energy stored in reactant bonds is crucial for determining the nature of chemical energy changes.

Endothermic and Exothermic Processes

Endothermic processes absorb heat, including separation of ions and phase changes from solid to gas.
Exothermic processes, such as combustion and salt formation, release heat, underscoring diverse energy dynamics in chemistry.

Sodium and Water Reaction

The reaction between sodium and water is notably exothermic, illustrating rapid energy release.

Conservation Principles

Conservation of mass and energy are crucial concepts, asserting that mass and energy of products equals that of reactants before and after reactions.

Description

Explore the principles of energy changes during chemical reactions and phase transitions in this flashcard set. Learn about the historical developments in understanding thermal energy and how it influences chemical processes. This resource will enhance your grasp of chemical thermodynamics and energy predictions.

Chemistry Unit 4 Lesson 2

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Questions and Answers

Chemical reactions are driven by changes in energy.

Who invented dynamite?

What type of reaction releases energy?

What type of reaction absorbs energy?

What is conserved during a chemical reaction?

Which of the following chemicals is used in dynamite?

Dynamite gets its energy from ______.

What happens during an exothermic reaction?

Which process absorbs heat?

Combustion reactions give off heat, so they are exothermic.

Hand warmers are examples of endothermic reactions.

Cold packs absorb heat by dissolving salts.

What type of reaction occurs when sodium reacts with water?

For any chemical reaction, the total energy in the reaction remains the same.

Energy changes do not occur during chemical reactions.