models of light, endo and exothermic reactions Flashcards
waves and particles
- A wave is a disturbance that travels through space, carrying energy
- Particles are countable pieces of a substance with particular properties.
Wave-particle duality
Sometimes light acts like a wave and sometimes a particle.
- In each situation either a wave or particle model works better to describe light.
- EM radiation is both a particle and a wave at the same time.
Wave action-reflection
reflect off a surface at the same angle it came in
EM radiation evidence-reflection
reflects off a surface at the same angle that it comes in.
Particles action- reflection
Bounce off a surface at the same angle that they come in.
Wave action- refraction
bends towards the perpendicular line when moving into a “slower” substance.
Particle action-refraction
bends away from the perpendicular line when moving into a “slower” substance.
EM radiation evidence- refraction
bends towards the perpendicular line when moving into a “slower” substance.
Wave action- diffraction
bend around corners, going behind barriers
Particle action- diffraction
don’t bend around barriers, go in straight lines
EM radiation evidence- diffraction
bends around corners, going behind barriers
Wave action- interference
interferes, adding or canceling through constructive and destructive interference.
Particle action- interference
they don’t interfere
EM radiation evidence- interference
Interferes, adding, or canceling through constructive and destructive interference.
Wave action- photoelectric effect, time delay
there should be a time delay between when the light first hits and the electrons get knocked off.
Particle action- photoelectric effect, time delay
have no time delay in ejecting electrons since they hit suddenly.
EM radiation evidence- photoelectric effect, time delay
there is no time delay.
Wave action- photoelectric effect, brightness
brighter light has more energy so it will give the electrons more energy and make them fly off faster.
Particle action- photoelectric effect, brightness
brighter light means more photons, which knocks off more electrons but doesn’t affect the energy.
EM radiation evidence- photoelectric effect, brightness
brighter light knocks off more electrons but doesn’t give them more energy to fly off faster.
Wave action- photoelectric effect, color
the color of the light has no effect on the electrons that are emitted from the metal.
Particle action- photoelectric effect, color
higher frequency light means photons have more energy so the electrons are ejected with more energy.
EM radiation evidence- photoelectric effect, color
color does matter, higher frequency light makes the electrons go faster.
The photoelectric effect
If visible light is shined on metals in specific conditions, the metal will absorb the light and emit electrons.
Exothermic reaction
a chemical reaction is exothermic if it gives off heat
Endothermic reaction
a chemical reaction is endothermic if it absorbs heat.
Chemical energy and thermal energy in chemical reactions
- In exothermic reactions the chemical energy decreases in the reaction and the thermal energy increases.
- In endothermic reactions the chemical energy increases in the reaction and the thermal energy decreases.
Chemical energy
Chemical energy is a type of potential energy stored in chemical bonds.
Making new chemical bonds
When new chemical bonds form atoms move with the attractive force. Therefore, when new chemical bonds form their potential energy drops.
Chemical bonds
Chemical bonds are attractive forces between atoms
Breaking old chemical bonds
When chemical bonds break, atoms move against the attractive force. Therefore, when old chemical bonds break their potential energy increases.
Rate of a chemical reaction
The rate of a chemical reaction is how quickly the reaction occurs
High and low reaction rates
Chemical reactions with a high reaction rate occur quickly
Chemical reactions with a low reaction rate occur slowly
Factors that can affect reaction rate
- Temperature
- Phase
- Concentration
- Catalysts
Temperature and reaction rate
- Increasing the temperature of a reaction speeds up the reaction rate
- Decreasing the temperature of a reaction slows the reaction rate
Phase and reaction rate
- In order for two substances to react, their particles must be in contact
Gases have the fastest reaction rate
Liquids have a slower reaction rate
Solids have the slowest reaction rate
Breaking solids and reaction rate
If solid reactants are broken up into smaller pieces more particles can come into contact and the reaction rate will be quicker.
Concentration
- The concentration of a substance is the amount of that substance in a certain space.
Concentration and reaction rates
- Increasing the concentration of a reactant speeds up the reaction rate
- Decreasing the concentration of a reactant slows the reaction rate
Catalysts and reaction rate
A catalyst is a substance that speeds up a chemical reaction without being used up. Using a catalyst increases the reaction rate.
