C6 - The Rate and Extent of Chemical Changes Flashcards
What is an example of a slow chemical reaction?
Rusting of iron.
Which type of reaction is faster, burning or explosions?
Explosions are faster.
How can you determine the speed of a reaction using a graph?
By recording the amount of product formed or reactant used up over time.
What does a steeper line on a reaction rate graph indicate?
A faster rate of reaction.
What happens to the slope of the graph over time?
It becomes less steep as the reactants are used up.
What do flat lines on a reaction graph indicate?
The reaction has finished.
What is required for particles to react according to collision theory?
Particles must collide with enough energy.
What two factors influence the rate of a chemical reaction?
- Collision frequency
- Energy transferred during a collision.
What is activation energy?
The minimum amount of energy needed for particles to react.
Fill in the blank: A successful collision is a collision that ends in the particles _______.
reacting to form products.
What happens to the rate of reaction if the frequency of collisions is doubled?
The rate doubles.
What must particles do to break the bonds in the reactants?
Collide with enough energy.
What are the four main factors affecting the rate of reaction?
- Temperature
- Concentration of a solution
- Surface area
- Presence of a catalyst
These factors influence how often particles collide and the energy of those collisions.
How does increasing temperature affect the rate of reaction?
Increases particle speed and collision frequency
Faster particles have more energy, leading to more successful collisions.
What is the effect of increasing the concentration of a solution on reaction rate?
More particles in the same volume lead to more frequent collisions
This applies similarly to gases when pressure is increased.
How does increasing the surface area of a solid reactant affect the reaction rate?
More area for collisions increases frequency of reactions
Breaking solids into smaller pieces enhances surface area to volume ratio.
What is a catalyst?
A substance that speeds up a reaction without being consumed
Catalysts lower activation energy by providing an alternative pathway.
What is the role of enzymes in biological reactions?
They act as biological catalysts
Enzymes facilitate reactions in living organisms.
True or False: A catalyst is part of the overall reaction equation.
False
Catalysts are not consumed and do not appear in the overall reaction equation.
Fill in the blank: The activation energy needed for a reaction can be decreased by using a _______.
[catalyst]
This allows reactions to occur more easily and at lower energy levels.
What happens to collision frequency when the pressure of a gas is increased?
Collisions become more frequent
Higher pressure means the same number of particles in a smaller space.
What does a rate of reaction graph show on the y-axis?
The amount of product formed or amount of reactant used up
The x-axis represents time.
How do you calculate the mean rate of reaction from a graph?
Mean rate = overall change in y-value ÷ total time taken
This can also be applied to find the mean rate between any two points in time.
What is the mean rate of reaction between 20 s and 40 s if the change in volume is from 15 cm³ to 19 cm³?
0.2 cm/s
Calculation: (19 cm³ - 15 cm³) ÷ 20 s = 0.2 cm/s.
What is the method to find the reaction rate at a particular point on the graph?
Draw a tangent to the curve at that point
The gradient of the tangent gives the rate of reaction.
How do you calculate the gradient of the tangent?
Gradient = change in y ÷ change in x
Use two easy-to-read points on the tangent line.
If the mass of reactant used up at 2.0 minutes is 1.4 g and at 5.0 minutes is 2.2 g, what is the rate of reaction?
0.27 g/min
Calculation: (2.2 g - 1.4 g) ÷ (5.0 min - 2.0 min) = 0.27 g/min.
True or False: The mean rate of reaction can only be calculated for the entire duration of the reaction.
False
The mean rate can also be calculated between any two points in time.
What is a reversible reaction?
A reaction that can go both ways, where products can react to form reactants again.
What happens to the concentrations of reactants during a reversible reaction?
The concentrations of reactants fall as they react.
What is dynamic equilibrium?
A state where both forward and backward reactions are occurring at the same rate, resulting in no overall change.
What is required for a reversible reaction to reach equilibrium?
The reaction must take place in a closed system.
What does a closed system mean in the context of reversible reactions?
None of the reactants or products can escape and nothing else can get in.
Does equilibrium mean that the amounts of reactants and products are equal?
No, equilibrium does not imply equal amounts of reactants and products.
What does it mean if the equilibrium lies to the right?
The concentration of products is greater than that of the reactants.
What does it mean if the equilibrium lies to the left?
The concentration of reactants is greater than that of the products.
What factors affect the position of equilibrium?
- Temperature
- Pressure (affects gases)
- Concentration of reactants and products
What happens to the equilibrium position when a reaction is heated?
Heating can shift the equilibrium to the right, favoring product formation.
What is the relationship between endothermic and exothermic reactions in reversible reactions?
If a reaction is endothermic in one direction, it will be exothermic in the other.
What is the thermal decomposition of hydrated copper sulfate an example of?
An endothermic reaction when heated, followed by an exothermic reaction upon adding water.
Fill in the blank: The energy transferred from the surroundings during an endothermic reaction is equal to the energy transferred to the surroundings during an _______ reaction.
exothermic
What does ‘anhydrous’ mean?
‘Without water’
What does ‘hydrated’ mean?
‘With water’
What is the effect of cooling a reaction that has reached equilibrium?
Cooling moves the equilibrium to the left, favoring reactant formation.
What is Le Chatelier’s Principle?
The idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change.
What happens to a reversible reaction if the temperature is decreased?
The equilibrium will move in the exothermic direction to produce more heat.
What is the effect of raising the temperature on a reversible reaction?
The equilibrium will move in the endothermic direction to try and decrease the temperature.
In the reaction N2 + 3H2 ⇌ 2NH3, which direction does the equilibrium shift if the temperature is decreased?
The equilibrium shifts to the right, producing more NH3.
What is the impact of changing pressure on an equilibrium involving gases?
Increasing pressure shifts the equilibrium towards the side with fewer gas molecules.
If the pressure is decreased in a gas equilibrium, what is the system’s response?
The equilibrium shifts towards the side with more gas molecules.
In the equation N2 + 3H2 ⇌ 2NH3, how many moles of gas are on the left side?
4 moles (1 of N2 and 3 of H2).
What happens when the concentration of reactants is increased in a reversible reaction?
The system tries to decrease it by making more products.
What is the system’s response if the concentration of products is decreased?
The system tries to increase it again by reducing the amount of reactants.
Fill in the blank: Reversible reactions attempt to _______ changes made to the system.
counteract
True or False: Le Chatelier’s Principle can be used to predict the effect of changes made to a reaction system.
True
What is organic chemistry primarily concerned with?
Compounds that contain carbon
Define a hydrocarbon.
A compound formed from carbon and hydrogen atoms only
Is CH3COOCH3 a hydrocarbon? True or False.
False
What type of bonds do alkanes contain?
All C-C single bonds
What is the general formula for alkanes?
C_nH_(2n+2)
Name the first four alkanes.
- Methane: CH4
- Ethane: C2H6
- Propane: C3H8
- Butane: C4H10
What is a displayed formula?
A drawing showing all the atoms and bonds in a molecule
How do hydrocarbon properties change as the carbon chain gets longer?
They become less runny, less volatile, and less flammable
What is the relationship between carbon chain length and viscosity?
Shorter carbon chains are less viscous
What type of hydrocarbons are used as ‘bottled gases’?
Short chain hydrocarbons with lower boiling points
What is produced during the complete combustion of hydrocarbons?
- Carbon dioxide
- Water vapour
- Energy
Complete the equation: hydrocarbon + oxygen → ______ + water.
carbon dioxide
During combustion, what happens to carbon and hydrogen in hydrocarbons?
They are oxidised
What is the balanced equation for the complete combustion of methane (CH4)?
CH4 + 2O2 → CO2 + 2H2O
How many hydrogen atoms are in one molecule of methane?
Four
What is oxidation in the context of combustion?
The gain of oxygen
