Chapter 12: Explaining Chemical Changes: Flashcards
What else to look into?
Is a bomb calorimeter an isolated system and is a coffee cup calorimeter a closed system? Know intermediates for test?
What are some ways of increasing the rate of a reaction?
Increasing the temperature, increasing the pressure/concentration of a gas, increasing the concentration of solution, increasing the surface area of a solid/liquid (can’t change concentration), adding catalyst.
What are the main ideas of the collision-reaction theory?
- A chemical sample consists of entities (atoms/ions, and molecules) that are in constant random motion, rebounding elastically from collisions with each other. 2. A chemical reaction must involve a collision between reacting entities. 3. An effective collision requires the correct orientation of the colliding entities so that bonds may be broken and rearranged. 4. An effective collision also requires sufficient energy to have the potential to react.
What happens during an elastic collision?
Kinetic energy is conserved during elastic collisions. Ineffective collisions involve entities that rebound elastically from each other.
What is activation energy?
An energy barrier that must be overcome for a chemical reaction to occur. Entities must somehow reach this minimum energy before reacting- and the input energy (which supplies activation energy) may be in the form of heat, light, or electricity.
What does the activation energy/potential energy diagram of a successful collision/reaction look like?
The potential energy increases as input energy is added so that entities may reach activation energy, and once they do so the potential energy is converted to kinetic energy as the bonds have been rearranged.
What is the activated complex?
The chemical entity containing collided reactants at the maximum potential energy point along energy pathway.
What is bond energy?
The energy required to break a chemical bond. It is also the energy released when a bond is formed.
When considering bond energy, what is implied by an endothermic reaction?
An endothermic reaction implies that more energy was absorbed to break the bonds of the reactants than was released when the bonds between the products were formed.
When considering bond energy, what is implied by an exothermic reaction?
An exothermic reaction implies that more energy was released when bonds were formed in the products than is needed to break bonds in the reactants.
How to find the amount of energy needed to break bonds between the reactants from a potential energy diagram?
The energy needed to break the bonds in reactants is equal to the activation energy, therefore it can be found by finding the difference between the activated complex and the energy of reactants.
How to find the amount of energy needed to form bonds in the products from a potential energy diagram?
The amount of energy needed to form bonds in the products can be found by finding the difference between the activated complex and the potential energy of the products.
What are the 4 methods for predicting/explaining an enthalpy change?
- Calorimetry; when the change in enthalpy equals the change in thermal energy. 2. Hess’ law; When the change in enthalpy equals the sum of enthalpy changes. 3. Molar enthalpies of formation; When the change in enthalpy equals the sum of enthalpies of formation of the products minus the sumo of enthalpies of formation of the reactants. 4. Bond energies: The change in energy equals the energy released from bond making minus the energy required for bond breaking.
What is a catalyst?
A substance that increases the rate of a reaction WITHOUT being consumed itself in the overall process. The chemical composition and amount of a catalyst are IDENTICAL at the start and the end of a reaction.
How does a catalyst operate?
A catalyst reduces the quantity of energy required to start a reaction, and results in a catalyzed reaction having a greater percent yield.
