[C6] The rate and extent of chemical change

What is rate of reaction?

A measure of how quickly reactants turn into product

What equations are used to calculate the mean rate of reaction? (2)

quantity of reactant used ÷ time

quantity of product formed ÷ time

What are the units of rate of reaction? (3)

g/s

cm³/s

mol/s

What are the usual units for mass (in chemistry)?

g

What are the units for volume

cm³

A steep gradient on a rate of reaction graph shows what?

fast reaction

What does it mean when a graph showing rate of reaction levels off?

the reaction is complete and no more product is produced

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] How can the actual rate of reaction be determined from a rate of reaction graph?

draw a tangent to the curve, measure the gradient of the tangent

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What is the equation for measuring the gradient?

change in y ÷ change in x

What is concentration?

The number of particles in a given volume

What is pressure?

A measure of how close together gas particles are

What is surface area?

The area of a solid that is exposed to the surface

How could you increase the surface area of a solid reactant?

Break it into smaller pieces

Which has a larger surface area: 10 g of magnesium ribbon or 10 g of magnsium powder?

magnesium powder

What happens to the rate of a reaction when the concentration of reactants in solution is increased?

rate increases

What happens to the rate of a reaction when the pressure of reacting gases is increased?

rate increases

What happens to the rate of a reaction when the temperature is increased?

rate increases

What happens to the rate of a reaction when the surface area of solid reactants increases?

rate increases

What happens to the rate of a reacton when a solid reactant is broken into smaller pieces?

rate increases

What methods can you use to collect a gas? (2)

Collect in gas syringe

collect in inverted measuring cylinder under water

What piece of apparatus should be used to measure 20 cm³ of acid?

Measuring cylinder

When will solutions turn cloudy?

When an insoluble solid is produced

Why can measuring the time taken for a solution to turn cloudy indicate the rate of reaction? (2)

the solution turns cloudy when the product is formed

Measuring the time allows us to do 𝙦𝙪𝙖𝙣𝙩𝙞𝙩𝙮 𝙤𝙛 𝙥𝙧𝙤𝙙𝙪𝙘𝙩 𝙛𝙤𝙧𝙢𝙚𝙙 ÷ 𝙩𝙞𝙢𝙚

What are the independent and dependent variables in the investigation: 𝑨 𝒔𝒕𝒖𝒅𝒆𝒏𝒕 𝒎𝒆𝒂𝒔𝒖𝒓𝒆𝒔 𝒕𝒉𝒆 𝒕𝒊𝒎𝒆 𝒕𝒂𝒌𝒆𝒏 𝒇𝒐𝒓 𝒂 𝒄𝒓𝒐𝒔𝒔 𝒕𝒐 𝒅𝒊𝒔𝒂𝒑𝒑𝒆𝒂𝒓 𝒘𝒉𝒆𝒏 𝒅𝒊𝒇𝒇𝒆𝒓𝒆𝒏𝒕 𝒄𝒐𝒏𝒄𝒆𝒏𝒕𝒓𝒂𝒕𝒊𝒐𝒏𝒔 𝒐𝒇 𝒔𝒐𝒅𝒊𝒖𝒎 𝒕𝒉𝒊𝒐𝒔𝒖𝒍𝒇𝒂𝒕𝒆 𝒂𝒓𝒆 𝒖𝒔𝒆𝒅? (2)

Independent: concentration of sodium thiosulfate

Dependent: time taken for cross to disappear

What variables should be controlled in the investigation: 𝑨 𝒔𝒕𝒖𝒅𝒆𝒏𝒕 𝒎𝒆𝒂𝒔𝒖𝒓𝒆𝒔 𝒕𝒉𝒆 𝒕𝒊𝒎𝒆 𝒕𝒂𝒌𝒆𝒏 𝒇𝒐𝒓 𝒂 𝒄𝒓𝒐𝒔𝒔 𝒕𝒐 𝒅𝒊𝒔𝒂𝒑𝒑𝒆𝒂𝒓 𝒘𝒉𝒆𝒏 𝒅𝒊𝒇𝒇𝒆𝒓𝒆𝒏𝒕 𝒄𝒐𝒏𝒄𝒆𝒏𝒕𝒓𝒂𝒕𝒊𝒐𝒏𝒔 𝒐𝒇 𝒔𝒐𝒅𝒊𝒖𝒎 𝒕𝒉𝒊𝒐𝒔𝒖𝒍𝒇𝒂𝒕𝒆 𝒂𝒓𝒆 𝒖𝒔𝒆𝒅? (5)

volume of sodium thiosulfate

concentration of hydrochloric acid

volume of hydrochloric acid

same cross

temperature

What are the independent and dependent variables in the investigation: 𝑨 𝒔𝒕𝒖𝒅𝒆𝒏𝒕 𝒎𝒆𝒂𝒔𝒖𝒓𝒆𝒔 𝒕𝒉𝒆 𝒗𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝒈𝒂𝒔 𝒑𝒓𝒐𝒅𝒖𝒄𝒆𝒅 𝒘𝒉𝒆𝒏 𝒅𝒊𝒇𝒇𝒆𝒓𝒆𝒏𝒕 𝒄𝒐𝒏𝒄𝒆𝒏𝒕𝒓𝒂𝒕𝒊𝒐𝒏𝒔 𝒐𝒇 𝒉𝒚𝒅𝒓𝒐𝒄𝒉𝒍𝒐𝒓𝒊𝒄 𝒂𝒄𝒊𝒅 𝒂𝒓𝒆 𝒖𝒔𝒆𝒅?

Independent: concentration of hydrochloric acid Dependent: volume of gas produced

What is collision theory?

the theory that for chemical reactions to occur reacting particles must collide with sufficient energy

What is the activation energy?

the minimum amount of energy that reacting particles must collide with for a reaction to occur

What happens if reacting particles collide with energy less than the activation energy?

no reaction - they stay as reactants

What happens if reacting particles collide with energy greater than or equal to the activation energy?

they are converted into products

What does the term 𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 𝒐𝒇 𝒄𝒐𝒍𝒍𝒊𝒔𝒊𝒐𝒏𝒔 mean?

the number of collisions in a given amount of time (e.g. collisions per second)

How can you increase the rate of a reaction? (2)

increase the frequency of collisions

increase the energy of collisions

Why does increasing the surface area increase the rate of a reaction? (3)

increases the number of particles available for collisions

increases the frequency of collisions

which increases the chances of successful collisions with energy higher than the activation energy

Why does increasing the concentration of reactants increase the rate of a reaction? (3)

Increases the number of particles in a given volume

Increases the frequency of collision

Increases the chances of successful collisions with energy higher than the activation energy

Why does increasing the pressure of reacting gases increase the rate of a reaction? (3)

Causes particles to be closer together

Increases the frequency of collisions

Increases the chances of successful collisions with energy higher than the activation energy

Why does increasing the temperature increase the rate of a reaction? (3)

Increases the kinetic energy of the particles

Increases the frequency and energy of collisions

Increases the chances of successful collisions with energy higher than the activation energy

What happens to the rate of the reaction if the frequency of collisions doubles?

rate doubles

What happens to the rate of a reaction if the frequnecy of collisions is halved?

rate halves

What are catalysts?

Substances that increase the rate of chemical reactions without getting used up themselves

Why are catalysts not included in chemical equations?

they are not used up or produced in chemical reactions

Why does using a catalyst increase the rate of a reaction? (2)

Catalysts provide a different pathway for the reaction with a lower activation energy

More collisions have energy higher than the activation energy

What does a reaction profile for a catalysed reaction look like?

a profile with a lower energy reaction pathway for the reaction with a catalyst

What does this symbol ⇌ mean?

a reversible reaction

What is a reversible reaction?

A reaction in which reactants react to form products and the products can react to form the reactants

How can the direction of a reversible reaction be changed?

by changing the conditions (e.g. heat for one direction, cool for the other direction)

What is an exothermic reaction?

A reaction that transfers energy to the surroundings

What is an endothermic reaction?

A reaction that takes in energy from the surroundings

If a reversible reaction is exothermic in one direction, what type of reaction is the reverse reaction?

Endothermic

What is dynamic equilibrium?

When the rate of the forward reaction is exactly the same as the rate of the reverse reaction

What conditions are needed for dymanic equilibrium to be reached? (2)

A closed system

Prevents the escape of reactants and products

What is a closed system?

Apparatus set up in a way that prevents anything (e.g. reactants and products) from entering or leaving

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] How does a system at equilibrium respond to changes? (3)

The system will stop being at equilibrium

The rate of either the forward or the reverse reaction will increase

Until a new equilibrium is reached

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What is Le Chatelier's Principle?

If the conditions of a system at equilibrium change, the system will respond to counteract the change

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the temperature increases, how will a system at equilibrium respond?

System will decrease the temperature

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the temperature of a system at equilibrium decreases, how will the system respond?

System will increase the temperature

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the temperature of a system at equilibrium increases, will the exothermic or endothermic reaction be favoured?

Endothermic reaction

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the temperature of a system at equilibrium decreases, will the exothermic or endothermic reaction be favoured?

Exothermic reaction

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the concentration of a reactant is increased in a system at equilibrium, which reaction is favoured?

The forward reaction

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the concentration of a reactant is decreased in a system at equilibrium, which reaction is favoured?

The reverse reaction

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the concentration of a product is increased in a system at equilibrium, which reaction is favoured?

The reverse reaction

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the concentration of a product is decreased in a system at equilibrium, which reaction is favoured?

The forward reaction

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the rate of the forward reaction increases in a reversible system, what will happen to the concentration of reactants and products? (2)

Concentration of reactants decrease

Concentration of products increase

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the pressure is increased in a system at equilibrium, which reaction is favoured?

the reaction which produces fewer molecules of gas

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] If the pressure is decreased in a system at equilibrium, which reaction is favoured?

the reaction which produces more molecules of gas

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] 𝗡₂𝗢₄ (𝗴) ⇌ 𝟮 𝗡𝗢₂ (𝗴) Which reaction will be favoured if the pressure increases?

the reverse (backwards) reaction as there are fewer gaseous molecules on the left side

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What does yield mean?

How much of a substance is produced