Ch - 7 (Chemical Energetics) Flashcards
When do exothermic and endothermic reactions take place?
Chemical bonding
What does chemical bonding involve?
The transfer of thermal energy in or out.
What are the 2 key terms involved in the transfer of thermal energy?
- System (What happens in the chemical reaction)
- Surroundings (anything other than the chemicals reacting)
What happens in an exothermic reaction?
- Thermal energy is transferred from the system to the surroundings.
What happens to the surrounding temp. in an exothermic reaction?
Temp. increases
Why is the energy change in an exothermic reaction negative?
- The energy is transferred from the chemical energy store of the chemical system to the surroundings
- Energy of the system falls.
What are examples of an exothermic reaction?
- Combustion
- Oxidation
- Neutralisation reactions.
- Handwarmers
- Self-heating cans of food n drinks
What happens in an endothermic reaction?
Thermal energy is transferred from the surroundings into the systems
why is the energy change in an endothermic reaction positive?
This energy is transferred to the chemical energy story of the chemical systems
- Energy of the system increases.
what are examples of endothermic reactions?
- Electrolysis
- Thermal decomposition reactions
- Photosynthesis First stages
- Cold packs
What are reaction pathways diagrams or energy level diagrams?
Graphical representation of relative energies of the reactants and products in chemical reactions.
What represents the overall energy change of a reaction?
The diff. in height between the energy of reactants and products
What represents the activation energy (Ea)?
The initial increase in energy.
Define Ea.
Minimum energy that colliding particles must have in order to react.
How can we identify a reaction pathway diagram for an exothermic reaction?
- Energy of the product is lower than the reactants
- (As thermal energy has been transferred to the surroundings)
