The rate & Extent of chemical change (seneca) Flashcards
In industry, making the required amount of product as cheaply as possible maximises
all-important profit.
Faster reactions are often better as they …
yield more product in a given amount of time.
A chemical reaction’s rate tells us how …
quickly reactants are converted into products.
It may be ——- to generate the conditions for very fast reactions.
expensive
It may be expensive to ———- for very fast reactions.
generate the conditions
reaction rates used in industry are the result of a trade-off between …
speed, cost and safety.
There can be —– concerns associated with very fast reactions.
safety
Rate of reaction =
change in y/ change in x
Rates of reactions at specific times can be calculated using graphs. Describe how.
-Draw a tangent to the curve (a straight line that touches the curve at just 1 point).
-Work out the tangent’s gradient.
Importantly, particle collisions must happen with …
enough energy
Particles must —— for chemical reactions to happen.
collide
We can increase the rate of a reaction by …..
This can be achieved by ….
- increasing the frequency (number) of collisions and/or the energy of reactant particles.
- changing lots of different factors.
Faster reactions are often better as they produce —– product in a given amount of time.
more
What are the steps in calculating reaction rates from graphs?
-Draw a tangent
-Calculate its gradient
what is collision theory?
The theory that explains how chemical reactions occur and why they occur at different rates.
what is the theory that explains how chemical reactions occur and why they occur at different rates called?
Collision theory
Increasing the concentration increases…
This ——— the rate of reaction.
- the collision frequency
- increases
Increasing pressure is like …
increasing the concentration.
Increasing the pressure of gas reactants ——- the rate of reaction.
increases
Increasing the temperature ——- the rate at which collisions happen.
increases
Increasing the temperature 1 the energy of reactant particles. This means that a 2 proportion of the particles will have 3 energy than the activation energy that is needed.
- increases
- greater
- more
Using temperature to increase 1. and 2. , these lead to 3. This 4. the rate of reaction.
- the rate of collisions
- the energy of reactant particles
- more successful collisions
- increases
Increasing the surface area (of solid reactants ) ——- the collision frequency. This ——- the rate of reaction.
increases
(both answers)
Increasing the surface area (of solid reactants) is often done by …
breaking up solids into smaller lumps (e.g. powders).
This increase in surface area to volume ratio makes sure that …
more particles are exposed to attack.
Substances that increase a chemical reaction’s rate without reducing in quantity during the reaction are called …
catalysts.
what are catalysts?
Substances that increase a chemical reaction’s rate without reducing in quantity during the reaction.
Increasing the temperature of a reaction causes the frequency of collisions and the energy of reactant particles to increase, meaning that a higher percentage of the particles will have energy in excess of the ——- energy.
activation
Catalysts are not used up during chemical reactions. This means that:
-They can be reused indefinitely.
-They are not found in chemical equations.
Catalysts will often need 1. , which has 2. for 3.
- cleaning or regenerating
- knock-on effects
- energy expenditure and environmental impact.
Different catalysts are appropriate for different reactions:
-Iron is used in the process that makes ammonia.
-Platinum and palladium are used in catalytic converters in cars.
-Enzymes catalyse reactions in biological systems.
What form do catalysts come in?
Catalysts often come as powders, pellets or fine gauzes because these types of substance have particularly high surface areas.
are catalyst used up in reactions?
no
What are the reprecussions (but good tho) of catalysts not being used up?
-They can be reused indefinitely
-They are not found in chemical equations
Catalysts increase the
—- of chemical reactions by lowering the activation energy. They do this by providing a …
- rate
- different reaction pathway.
Despite the fact that some catalysts are expensive precious metals (e.g. platinum and palladium), they are often cost-effective to use because,
-a small amount can speed up a reaction by a lot.
It may be cheaper to pay for the catalyst at the start and increase the rate of reaction after that.
-Paying for a catalyst may be cheaper than paying for the energy needed to increase either temperature or pressure.
By reducing the necessary temperatures and/or pressures, ——– fossil fuels need to be burned.
This means that …
- fewer
- we can reduce our negative environmental impact.
Many catalysts are ———-, and these can …
toxic (e.g. transition metals)
escape into the environment and contaminate ecosystems
Why does the use of catalysts in industry benefit the environment?
Reduces burning of fossil fuels
Some chemical reactions can proceed in both forwards and backwards directions. We describe these reactions as …
reversible.
A + B ⇌ C + D
The reactants (——) can combine to give…
A + B
the products (C + D).
A + B ⇌ C + D
The products (—–) can combine to give …
C + D
the reactants (A + B).
If the forwards reaction is exothermic (transfers energy from reactants to the environment), the backwards reaction will be …
endothermic (transfers energy from the environment to the reactants).
If the forwards reaction is endothermic (transfers energy from the environment to the reactants), the backwards reaction will be
exothermic (transfers energy from reactants to the environment)
—- is conserved during chemical reactions.
Energy
The energy released/absorbed by the forward reaction will be …
exactly equal to the energy absorbed/released by the backward reaction.
Which type of reaction transfers energy from the reactants to the environment?
exothermic
what is a example of a reversible reaction ?
ammonium chloride ⇌ ammonia + hydrogen chloride
When reversible reactions happen within a closed system, ——— will eventually be reached.
a dynamic equilibrium
A closed system is a …
system where reactants and products can neither be added nor removed.
A ——– is a system where reactants and products can neither be added nor removed.
closed system
At dynamic equilibrium, the rates of the forwards and backwards reactions are …
equal.
At ———–, the rates of the forwards and backwards reactions are equal.
dynamic equilibrium
The equilibrium is —– because both the forward and backward reactions are still taking place.
dynamic
The equilibrium is dynamic because …
both the forward and backward reactions are still taking place.
The concentrations of reactants and products —— change when a reaction is at dynamic equilibrium.
do not
What do we call a system in which reactants and products can neither be added nor removed?
closed system
what is a equilibrium?
when the rate of the forward reaction equals the rate of the backward reaction.
Changing the conditions in a reversible reaction affects …
the position of equilibrium.
The conditions in a reversible reaction determine …
the relative quantities of the different reactants and products in a reaction at equilibrium.
Le Chatelier’s principle says that if any of the conditions of a reversible reaction at equilibrium are changed, the closed system will …
adapt to counteract whatever has changed.
What process states that ‘if any of the conditions of a reversible reaction at equilibrium are changed, the closed system will adapt to counteract whatever has changed’?
Le Chatelier’s principle
Le Chatelier’s principle says that if …
any of the conditions of a reversible reaction at equilibrium are changed, the system will adapt to counteract whatever has changed.
Le Chatelier’s principle is used to …
predict the outcome of any changes imposed on a closed system at equilibrium.
If a reversible reaction takes place in a closed system dynamic, equilibrium will be …
reached
Dynamic equilibrium is dynamic because,
it is both the forward and backward reactions still take place
What determines the relative amounts of the substances involved in a reaction at equilibrium?
the conditions of the reaction
what happens to energy during chemical reactions?
it is conserved
At equilibrium, both forward and backward reactions still happen, but the ———- of reactants and products remain constant. So, we describe the equilibrium as …
- concentrations
- dynamic
Changing the temperature for a reaction at equilibrium takes —-. The system will ….
- the system out of equilibrium
- react to try and restore the equilibrium.
During reversible reaction, decreasing the temperature, the position of equilibrium will shift in the ——–direction.
exothermic
During reversible reaction, decreasing the temperature, the position of equilibrium will shift in the exothermic direction.
The amount of products generated by the exothermic reaction will 1.
The amount of products generated by the endothermic reaction will 2.
- increase
- decrease
During reversible reaction, increasing the temperature, the position of equilibrium will shift in the ——–direction.
endothermic
During reversible reaction, increasing the temperature, the position of equilibrium will shift in the endothermic direction.
The amount of products generated by the endothermic reaction will 1.
The amount of products generated by the exothermic reaction will 2.
- increase
- decrease
Pressure changes only affect reactions that involve …
gases
To predict what happens after a change in pressure, we must …
look at balanced equations to see how many gas molecules are on each side of the equation.
When the pressure is increased, the position of equilibrium will shift to favour the …
reaction that produces the fewest gas molecules.
When the pressure is decreased, the position of equilibrium will shift towards the …
side of the reaction that produces the most gas molecules.
(most moles)
The following reversible reaction is at equilibrium: A(g) ⇌ B(g) + C(g). What happens if the pressure is increased?
the backwards reaction
Pressure changes only affect reactions involving reactants in what state?
gas
Changing the concentration of any reactant or product takes the ——. The system will react to …
- system out of equilibrium
- try to restore the equilibrium.
Increasing the concentration of a reactant,this will shift the position of equilibrium towards the …
products
Increasing the concentration of a product the position of the equilibrium will shift towards the …
reactants.
what happens when the pressures decreases in a reversible reaction?
The position of equilibrium will shift to favour the reaction that produces the most gas molecules.
what happen when the pressures increases in a reversible reaction?
The position of equilibrium will shift to favour the reaction that produces the fewest gas molecules.
What is a potential drawback of a fast rate of reaction in industry?
- Expensive to generate conditions for a fast reaction
- Safety concerns associated with very fast reactions
what graphs could be used to work out the rate of reaction from the gradient?
- concentration of reaction (y) vs time (x)
- mass of product (y) vs time (x)
Why do catalysts often come as powder?
Powders have a high surface area
In a specific reversible reaction, the forward reaction is exothermic and the backward reaction is endothermic.
The energy change of the forward reaction is ———- to the backwards reaction.
opposite and equal
