Topic 7 - Rates of Reaction and Energy Changes

Question 1

What is the rate of reaction?

Answer 1

how quickly a reaction happens

Question 2

What is the equation for rate of reaction?

Answer 2

Amount of reactants used or amount of products used / time

Question 3

What are the 3 examples rate of reaction can be mesured?

Answer 3

Precipitation
Change in mass ( Usually gas given off)
Volume of gas given off

Question 4

Precipitation

Mesuring Rate of reaction

Answer 4

• works when mixing two clear solutions, that precipitate once reacted
• Mix the two and place the flask on a surface with a mark
• Observe how long it takes for the mark to be obscured through the precipitate

This result if subjective

Question 5

Change in mass ( usually given off)
Experemnt of rate of reaction

Answer 5

Rate of reaction that produces gas using a balance
The quicker the mass/ gas is lost, the quicker the reaction.
The reaction has finished once the mass stops changing
You can plot the results of mass aganst time

If the gas is harmfull, use a gas cupboard

Question 6

The volume of gas given off ( rate of reaction experement )

Answer 6

Involves the use of gas syringe to mesure gas given off
The more gas given off during a time set interval, the faster the reaction. the reaction is finished when no more gas is produced
Graph of gas volume/ time elapsed

Use the rightsize of syringe, if too much gas can blow the plunger off

Question 7

What is an exothermic reaction?

Answer 7

A reaction which gives out energy, usually in the form of heat, causing a rise in temp to the surroundings

Question 8

What is an endothermic reaction?

Answer 8

A reaction which absorbs energy, usually in the form of heat, causing a fall in temp to the surroundings

Question 9

What does an exothermic reaction look like on an energy/ time graph?

Answer 9

Reactants above products, energy is given out, lump leading down

Question 10

What does an endothermic reaction look like on an energy/ time graph?

Answer 10

Reactants below products, energy is taken in, lump leading up

Question 11

What is activation energy?

Answer 11

Minimum amount of energy needed for the bonds to break and a reaction to start

Question 12

Where is activation energy on and energy/time graph?

Answer 12

Between the reactants and highest peak of line

Question 13

what is the experiment for mesuring how surface area affects rate of reaction?

Answer 13

Set up a conical flask with dilute HCL and Marble chips, a gas syringe attached at the top
- Mesure the volume of gas produced using a gas syringe
- Take readings at regular time intervals
- Plot graph Time - x axis, Volume - Y axis
- Repeat with same mass of solution and marble but with the marble chips more crunched up
- Repeat with marble chalk

Question 14

What is the experiment for mesuring how temperature affects rate of reaction?

Answer 14

The reaction between sodium thiosulfate and hydrochloric acid both clear, colorless but form a yellow precipitate of sulfur
- Mesure out fixed volumes of each solution - mesuring cylinder
- Use a water bath to gently heat both solutions to desired temp
- Mix solutions in conical flask over paper with X marked on it, mesure the time taked for the X to be invisible
- Repeat at different temperatures

Question 15

What does rate of reaction depend on?

Answer 15

Collision frequency of reacting particles
- The more succesful collisions there are, the faster the reaction is
Energy transferred during a collision
-Particles need to collide with at least the activation energy for the collision to be succesfull

Question 16

If there are more particle collisions, what does this increase?

Answer 16

Rate of reaction

Question 17

What main 3 things affect rate of reaction?

Answer 17

Temperature
Concentration / Pressure
Surface Area / Smaller solid particles

Question 18

How does increasing the temperature increase rate?

Answer 18

• When temp is increased, the particles move faster - causes higher frequency of collisions.
• Also increases energy in collsions, as it makes the particles move faster.
  This creates a higher frequency of succesful collisions, increasing the rate of reaction

Question 19

How does increasing the Concentration / Pressure increase rate?

Answer 19

Concentration - Liquid
If a solution is more concentrated, it means there are more particles of reactant in the same volume. This makes collisions more likely
Pressure - Gas
Increasing pressure means that the particles are more crowded. This means the frequency of collisions between particles will increase, so reaction rate will also increase.

Question 20

How does increasing the Surface Area increase rate?

Answer 20

An increase in surface area to volume ratio. The particles will have more area to collide with, increasing frequency of collisions.

Question 21

How do catalysts affect rate of reaction?

Answer 21

Catalysts work by decreasing the activation energy needed for a reaction to occur.
They do this by providing an alternate reaction pathway that has a lower activation energy
As a result, more of the particles have at least the minimum amount of energy needed for a reaction to occur when particles collide.

Question 22

How are enzymes used in fermentation?

Answer 22

To produce alchohol, enzymes catalyse the reaction that converts sugars (e.g. Glucose) into ethanol and carbon dioxide.

Question 23

What is the experiment to mesure temperature changes?

Exothermic / Endothermic experiment

Answer 23

• Put a polystyrene cup into a large beaker of wool
• Add known volume of your first reagent to the cup
• Mesure initial temperatue of the solution
• Add mesured mass/ volume of your second reagent to the cup
• Put lid on cup - reduce and heat loss by evaporation
• Record max (exo) or Min (endo) temperature
• Calculate temperature change

Question 24

What does the wool do in the temperature change experiment?

Answer 24

Gives insulation to help limit energy transfer to or from the reaction mixture.

Question 25

How does the experiment to mesure temperature change when dissolving salts in water?

Exothermic or endothermic?

Answer 25

• Dissolving ammonium chloride decreases temp of reaction mixture - endothermic
• Dissolving calcium chloride causes the temperature of the solution to rise - exothermic

Question 26

How does the experiment to mesure temperature change when doing a neutralisation?

Exothermic or endothermic?

Answer 26

Acid + base -> Salt + water
Most neutralisations are exothermic apart from
Ethanoic acid + Sodium carbonate - Endothermic

Question 27

How does the experiment to mesure temperature change when doing a displacement reaction?

Exothermic or endothermic?

Answer 27

A more reactive compound displacing a less reactive one, this is accompanied by the release of energy, making it exothermic

Question 28

How does the experiment to mesure temperature change when doing a precipitation reaction?

Answer 28

Precipitation - insoluble solids produced by two solution
These are exothermic

Question 29

What happens to bonds durng a chemical reaction?

Answer 29

Old bonds are broken and new ones are formed

Question 30

What happens when bonds break, is this exothermic or endothermic?

Answer 30

Energy must be supplied to break exitsting bonds - making it an endothermic process

Question 31

What happens when bonds are formed, is this exothermic or endothermic?

Answer 31

Energy is released when bonds are formed, making it an exothermic process

Question 32

What is the balance in bond energies in an endothermic reaction?

Answer 32

The energy used to **break **bonds is greater than the energy released by forming them.

Question 33

What is the balance in bond energies in an exothermic reaction?

Answer 33

The energy released by bonds is greater than the energy used to break them

Question 34

What is the formula for bond energy calculations?

Answer 34

Overall energy change =
Energy required to break bonds - Energy released by forming bonds

Question 35

What does a positive or negative overall energy change mean?

Overall is related to the chemicals and not surroundings

Answer 35

Positive = Endothermic (takes in energy)
Negative = Exothermic (gives out energy)