Physical Chemistry Flashcards
(29 cards)
What is an exothermic reaction?
Releases heat energy to the surroundings usually causing a temperature increase
What is an endothermic reaction?
An endothermic reaction is one that absorbs heat energy from the surroundings usually causing a temperature decrease
Describe a simple calorimetry experiment for dissolving displacement and neutralisation
Measure the change in temperature / in a polystyrene cup
Describe a simple calorimetry experiment for combustion
Burn the fuel in a spirit burner underneath a copper can filled with water and measure temp change
Q = ?
(Chem)
Q = mcΔT
What do all the symbols stand for in Q = mcΔT?
Q = Heat energy transferred (J)
m = Mass of liquid
c = Specific heat capacity (J/g/°C)
ΔT = change in temperature (°C)
ΔH = ?
ΔH = -q/n
What does the peak on an energy level diagram represent?
The peak represents the activation energy (the minimum energy required for a reaction to occur)
What does a downward curve on an energy level diagram indicate?
Exothermic
What does an upward curve on an energy level diagram indicate?
Endothermic
What type of process is bond-breaking
Endothermic
What type of process is bond-making
Exothermic
Describe an experiment to investigate the effect of changes in surface area of a solid on rate of reaction
React marble chips with dilute HCl and measure gas produced. Repeat with smaller chips. More surface area = faster reaction.
When will particles react?
Collide
Enough energy
Correct orientation
What affects rate of reaction (on a molecular level)
Collision frequency
Energy transferred during collisions
What is a successful collision
A collision that ends in a reaction
What is the activation energy
The minimum energy needed to break bonds in the reactants and start the reaction
What four things influence the rate of reaction?
Temperature
Surface area
Concentration of solution/pressure
Presence of catalyst
Why does rate of reaction increase with temperature?
Particles have more energy, move faster, and collide more frequently with enough energy to react (more successful collisions)
Why does rate of reaction increase with concentration or pressure?
More particles per unit volume = more frequent collisions = higher rate of successful collisions
Why does rate of reaction increase with surface area?
More exposed particles = more frequent collisions = higher rate of successful collsions
Describe an experiment to investigate the effect of changes in concentration or pressure on rate of reaction
React magnesium ribbon with hydrochloric acid of different concentrations and measure the volume of hydrogen gas produced over time. Higher concentration = faster reaction
