Chemical Reactions | 7 Flashcards
(17 cards)
How would you Identify a PHYSICAL CHANGE
- Does not result in the formation of a new substance
- Possible the reverse the change
- The properties of elements stay
- Change can be temporary
(Changing state , making a mixture)
How would you Identify a CHEMICAL CHANGE
- Results in the formation of a new compound
- Chemical change is permanent
- New properties
- Can be sped up with a catalyst
What are the factors of rate of reaction
- Concentration
- Pressure
- Surface area
-Temperature
- Catalyst
Explain why these factors affect the rate of reaction the the way they do
When particles collide , there needs to be a certain amount of energy with it for a reaction to occur
These factors (excluding catalysts) increase the energy and therefore increase the successful collision and increases the rate of reactions
Describe and evaluate the different methods of investigating rate of reaction
Rates of reactions can be measured using the amount of product used, or
amount of product formed over time:
Rate of reaction = amount of reactant used
————————————-
Time
amount of product formed
————————————-
Time
Quantity of reactant or product can be measured by the mass in grams or
by a volume in cm3
if a gas is produced in a reaction, you can either collect the gas produced
in a gas syringe and measure the volume over time, or let the gas escape
and measure loss of mass over time
Units of rate of reaction may be given as g/s or cm3/s
Use quantity of reactants in terms of moles and therefore, units for rate
of reaction in mol/s
Repeat experiment multiple times with different independent variable to form a graph
i.e. : if you are measuring temperature do multiple experiments with diff temps
Describe collision theory in terms of number of particles per unit of volume and frequency of collisions
For a reaction to occur , reactant particles need to collide with each other.
For the products to be formed , the collision needs to have a minimum amount of energy associated with it (activation energy)
the collisions with the minimum amount of energy form the product and are successful collisions , the more particles per unit of volume , more collisions and therefore more successful collisions and more product which means a faster rate of reaction
What does the catalyst do and how
Increases rate of reaction and is unchanged at end of reaction
It lowers the activation energy of a reaction so more collisions are successful
What is the symbol for reversable reaction
⇌
When does chemical equilibrium occur
When a reversible reaction occurs in a closed system, equilibrium is reached
when the reactions occur at exactly the same rate in each direction.
Describe the effect of changing the conditions the hydrated and anhydrous compounds
When you heat a hydrated compound , it becomes anhydrous
when you add water to a anhydrous compound , it becomes hydrated
This can be observed in copper(II) sulfate
when it is hydrated it is blue and when it is anhydrous it is white
Predict and explain how changing condition in the reversible reaction alters position of equilibrium
If concentration of reactants is increased: position of equilibrium shifts
towards products (right) so more product is produced until equilibrium is
reached again
if concentration of products is increased: position of equilibrium shifts
towards reactants (left) so more reactant is produced until equilibrium is
reached again
Effect of changing pressure:
In gaseous reactions, an increase in pressure will favour the reaction that
produces the least number of molecules.
If temperature is increased: equilibrium moves in the direction of the
endothermic reaction (e.g. if forwards reaction is endothermic and
temperature is increased, equilibrium shifts right to produce more
product)
If temperature is decreased: equilibrium moves in the direction of the
exothermic reaction
State equation for haber process and sources of the materials needed
Nitrogen + Hydrogen ⇌ ammonia
N2 + 3H2 ⇌ 2NH3
Nitrogen is taken from the atmosphere by fractional distillation of liquid air
Hydrogen is taken from the reaction of methane and steam ( 750 ° C , 30 atm , nickel catalyst) for favorable equilibrium
Explain the conditions used in the Haber process
450° C , 200 atm , iron catalyst
high pressure favors the right side because it favors the reactions that produce the least molecules of gas
Reactions which are exothermic produced more products when temperature was low so it is carried out at 450° C , if it is lowered too much the rate of reaction would be too slow so 450° C was decided as the optimum middle ground
The catalyst does affects forward and backward reactions the same so the equilibrium is not affected , the reaction is just sped up
Explain the effect of Temperature on rate of reaction
causes an increase in collision rate and more of the
colliding molecules have sufficient energy, activation energy, to react, so rate of
reaction increases
Explain the effect of Surface area on rate of reaction
Increasing the surface area of solid reactants by grinding it into powder makes more particles exposed to the other reactant , so the frequency of collisions increases
Explain the effect of Concentration / Pressure on rate of reaction
Increasing concentration / pressure of reacting solutions increases the number of particles in the space , therefore it increases the frequency of collisions .
