Energy Changes + Quantitative Chemistry

Question 1

What is an exothermic reaction

Answer 1

When heat is transfered to the surroundings

Question 2

Examples of exothermic reactions

Answer 2

Combustion reactions
Many oxidation reactions
Most neutralisation reactions

Question 3

What is an endothermic reaction

Answer 3

When energy is taken from the surroundings

Question 4

Examples of endothermic reactions

Answer 4

Thermal decomposition reactions

Reactions of citric acid and sodium hydrogencarbonate

Question 5

Apparatus needed for required practicle: temperature changes in reacting solutions

Answer 5

Polystyrene cup
Thermometer
Measuring cylinder
Top pan balance
250 cm³ glass beaker

Question 6

Method for required practicle: temperature changes in reaction solutions, when reacting 2 solutions

Answer 6

1. Put polystyrene cup into beaker to make more stable
2. Measure appropriate amount of liquid for each solution
3. Place one liquid in cup
4. Record temp of solution
5. Add the other solution and record highest/ lowest temp obtained
6. Change the independent variable and repeat

Question 7

Method for required practicle: temperature changes in reacting solutions, when reacting a solid with a solution

Answer 7

1. Place polystyrene cup into beaker for stability
2. Measure appropriate amount of liquid from the solution
3. Measure appropriate amount of solid
4. Put solution in cup
5. Record temp of solution
6. Add solid and record highest/ lowest temp obtained
7. Change independent variable and repeat

Question 8

What could ur independent variable be for the required practicle: temp changes in reacting solutions

Answer 8

Concentration of the liquid
Surface area of the solid
Type of alkali/ acid
Type of metal/ metal carbonate

Question 9

What is a problem with the temperature change in reacting solutions practicle and how can u stop it

Answer 9

Unwanted heat transfer
Use a lid on the beaker to stop it

Question 10

2 hazards for the required practicle, what can happen and how to stop it

Answer 10

Dilute acids and alkalis,
May irritate skin or eyes,
Wear eye protection and rinse of when touched by it

Solutions of metal salts ,
Dangerous to environment,
Dispose of it as advised by pro

Question 11

Describe an exothermic reaction graph

Answer 11

Reactants start as a horizontal line near top of graph

When energy is released a line is drawn straight down

Products carry on the horizontal line but futher down

Question 12

Describe the graph of an endothermic reaction

Answer 12

Reactants start as a horizontal line near bottom of graph

When energy is absorbed draw a vertical line straight upwards

Products carry of horizontal line but futher up

Question 13

An endothermic reaction uses the process of ________ ______ which means heat is ______ ____

Answer 13

Breaking bonds
Taken in

Question 14

An exothermic reaction uses the process of _____ _____ which _______ _____ energy

Answer 14

Forming bonds
Gives out

Question 15

Hiw to calculate an energy change for a reaction using bond energies

Answer 15

Add together all the bond energies for the bonds in the reactants ( energy in)

Add together all the bond energies for the bonds in the products ( energy out)

Energy change = energy in - energy out

Question 16

Concentration in mol/ dm³ =

Answer 16

Amount of solute in mol ÷ volume in dm³

Question 17

1 dm³ =

Answer 17

1000 cm³

Question 18

How to multiply from mol/ dm³ to g/ dm³ and vise versa

Answer 18

Multiply by reletive formula mass

Divide by reletive formula mass

Question 19

Why use a polystyrene cup in the practicle

Answer 19

Slows heat loss from side and bottom