Chapter 17: Energy Changes Flashcards
Define the law of conservation of energy.
Energy cannot be created or destroyed. It can only be converted from one form to another.
Define an exothermic reaction.
An exothermic reaction is a reaction during which heat is released to the surroundings, causing a temperature rise.
What are the characteristics of exothermic changes?
When an exothermic reaction occurs,
1) heat is released from the reactants and transferred to the surroundings
2) the temperature of the reaction mixture rises
How does the temperature of a reaction mixture change when an exothermic change occurs?
Initially, the temperature of the reaction mixture rises until the highest temperature is reached. When the reaction is complete, the temperature of the reaction mixture falls until it reaches room temperature.
What are some examples of chemical reactions that involve exothermic changes?
1) Bond formation
2) Combustion
3) Neutralisation
4) Respiration
Define an endothermic reaction.
An endothermic reaction is a reaction during which heat is absorbed from the surroundings, causing a temperature drop.
What are the characteristics of endothermic changes?
When an endothermic reaction occurs,
1) heat energy is absorbed and transferred from the surroundings to the reactants
2) the temperature of the reaction mixture falls
How does the temperature of a reaction mixture change when an endothermic change occurs?
Initially, the temperature of the reaction mixture falls until the lowest temperature is reached. When the reaction is complete, the temperature of the reaction mixture rises until it reaches room temperature.
What are some examples of chemical reactions that involve endothermic changes?
1) Bond breaking
2) Dissolving of ammonium salts
3) Photosynthesis
4) Thermal decomposition
Define enthalpy change, and explain how to calculate it.
The enthalpy change represents the difference in energy content of the reactants and products.
Delta H = total energy of products (BF) - total energy of reactants (BB)
How can we tell if a reaction is exothermic based on its overall enthalpy change?
Exothermic reaction:
Total energy released during bond formation in products (-ve) > total energy absorbed during bond breaking in reactants (+ve)
How can we tell if a reaction is endothermic based on its overall enthalpy change?
Endothermic reaction:
Total energy released during bond formation in products (-ve) < total energy absorbed during bond breaking in reactants (+ve)
Define activation energy.
Activation energy is the minimum amount of energy that reactant particles must possess in order for a chemical reaction to occur.
Describe the bond breaking process.
Energy is absorbed to break the chemical bond between atoms.
Describe the bond formation process.
Energy is released to form something. Energy is given out when forming bonds.
