Section 5 - Physical Chemistry Flashcards
Definition of exothermic reaction:
gives out energy to surroundings, usually as heat
Definition of endothermic reaction:
takes energy from surroundings, there is a fall in temp in surroundings.
Enthalpy change
change of temp in a reaction
If reaction is exothermic enthalpy is . ..
negative, the reaction gives out energy
If reaction is endothermic enthalpy is . …
positive, the reaction takes in energy
Heat energy transferred equation:
Q = m x c x T
exothermic reactions
- condensing
- freezing
- oxidation
- combustion
- neutralisation
endothermic reactions
- melting
- boiling
- decomposition
- reactions of metals, hydrogen, carbonates + acids
Calorimetry definition
change in heat of a substance
Calorimetry formula
q=mcT
Particle collision theory
- Particles are constantly moving
- Chemical reaction to take place the reactants first have to collide
- Amount of activation energy is different depending on the ocasion
Activation energy definition
minimum amount of energy supplied to break bonds
RoR definition
Change that involves rearranging atoms from reactant molecules to form new products
RoR evidence
colour change, temp change, bubbles, precipitate formation
RoR grams
Quantity of products formed / time taken (s)
RoR cm(cubed)
quantity of reactants used / time taken (s)
Factors to change the speed of a reaction
Concentration
Temperature
Pressure
Surface Area
Catalysts
How does concentration affect?
- More particles in the same space means more collisions
- More collisions means more effective collisions
- If you double the concentration you double the number of collisions
How does temperature affect?
- particles when heated gain kinetic energy
- When they move faster they collide more frequently
How does surface area affect?
- Smaller particles increase surface area
- more collisions happen because particles are more likely to collide
How does catalysts affect?
- reduce activation energy needed for a reaction
- less activation energy means more effective collisions
- They dont work on all reactions.
Rate of chemical reaction depends on
- Collision frequency of reacting particles
- energy tranferred during a collision
What is a reversible reaction?
products of a reaction can react with each other and convert back to the reactants
Example of reversible reaction
thermal decomposition of ammonium chloride
