Energetics

Question 1

Define an exothermic reaction

Answer 1

a reaction that gives out energy to the surroundings

Question 2

Define an endothermic reaction

Answer 2

a reaction takes in energy from the surroundings

Question 3

Define in system

Answer 3

within reaction

Question 4

Define surroundings

Answer 4

outside reaction

Question 5

What represents the activation energy for energy profile diagram

Answer 5

the arrow from the reactants energy level to the peak

Question 6

What does exothermic reactions reactants and products in an energy profile diagram

Answer 6

The energy level of the products is less than the energy level of the reactants. energy has been transferred to surroundings

Question 7

What are the endothermic reactions reactants and products in an energy profile diagram

Answer 7

Energy level of the products is more than then the energy level of the reactants as energy has been transferred from the surroundings to the product

Question 8

An application of exothermic reactions

Answer 8

hand warmers

Question 9

application of endothermic reactions

Answer 9

sports injury packs

Question 10

examples of exothermic reactions

Answer 10

oxidation reactions, combustion reactions and neutralisation reactions

Question 11

examples of endothermic reactions

Answer 11

thermal decomposition of metal carbonates, reactions of acids with metal hydrogencarbonates

Question 12

What is the equation for energy change

Answer 12

energy change = mass of solution (g) * heat capacity (c) * temp. change

Question 13

What are the steps to work out change in heat energy

Answer 13

1) Use this equation to calculate energy change
2) Work out moles of reactants used
3) Divide q by the number of moles of the reactant not in excess to give change in heat. (-q)/n=change in heat (j,mol-1 )
4) Add a sign and unit, divide by a thousand to convert jmol -1 to Kjmol -1

Question 14

What is the relationship between adding sodium hydroxide and temp.

Answer 14

Graph shows as sodium hydroxide added, temp. increases. This is as more sodium hydroxide added more reacts and more heat is released as it is an exothermic reaction

Question 15

Why does the temp. level off after a certain temp.

Answer 15

• At a certain volume maximum temp. levels off as sodium hydroxide is in excess now and not able to react

Question 16

Why may the temp. decrease after a certain point

Answer 16

May decrease after this point as we are adding more and more solution so energy will be spread out so max temp. decreases

Question 17

Describe how you would investigate temp. change using the neutralisation reaction of HCL and sodium hydroxide

Answer 17

1) Measuring cylinder to measure 30cm of dilute HCL
2) Transfer acid into polystyrene cup and put it into a beaker
3) Thermometer to measure temp. Of acid
4) Use measuring cylinder to measure 5cm2 of sodium hydroxide and add it to the solution
5) Thermometer and lid added with bulb of thermometer must be in lid and read highest temp.
6) Rinse out and dry polystyrene cup and repeat experiment but increasing 5cm2 of sodium hydroxide each time until 40cm2
7) Then do it again to calculate a mean

Question 18

What happens to bonds during a chemical reaction

Answer 18

• Energy must be supplied to break bonds in the reactants

- Energy is released when bonds in the products are made

Question 19

how do you work out the energy change of a reaction

Answer 19

• Energy Change of a reaction = Bonds broken – Bonds formed

Question 20

Why do exothermic reactions have a negative energy change

Answer 20

more energy is released in making new bonds than is needed to break bonds as energy is released to surroundings. Thus as -ve overall energy change

Question 21

Why do endothermic reactions have a positive energy change

Answer 21

• Endothermic reactions; more energy is needed to break bonds than is released making new bonds. Thus +ve overall change