# Topic: Energetics (D)

## 3:01 know that chemical reactions in which heat energy is given out are described as exothermic, and those in which heat energy is taken in are described as endothermic

Exothermic: chemical reaction in which heat energy is given out.

Endothermic: chemical reaction in which heat energy is taken in.

(So, in an exothermic reaction the heat exits from the chemicals so temperature rises)

## 3:02 describe simple calorimetry experiments for reactions such as combustion, displacement, dissolving and neutralisation

Calorimetry allows for the measurement of the amount of energy transferred in a chemical reaction to be calculated.

EXPERIMENT1: Displacement, dissolving and neutralisation reactions

Example: magnesium displacing copper from copper(II) sulfate

Method:

1. 50 cm3 of copper(II) sulfate is measured and transferred into a polystyrene cup.
2. The initial temperature of the copper sulfate solution is measured and recorded.
3. Magnesium is added and the maximum temperature is measured and recorded.
4. The temperature rise is then calculated. For example:
Initial temp. of solution (oC)Maximium temp. of solution (oC)Temperature rise (oC)
24.256.732.5

Note:  mass of 50 cm3 of solution is 50 g

The cup used is polystyrene because:

polystyrene is an insulator which reduces heats loss

EXPERIMENT2: Combustion reactions

To measure the amount of energy produced when a fuel is burnt, the fuel is burnt and the flame is used to heat up some water in a copper container

Example: ethanol is burnt in a small spirit burner

Method:

1. The initial mass of the ethanol and spirit burner is measured and recorded.
2. 100cm3 of water is transferred into a copper container and the initial temperature is measured and recorded.
3. The burner is placed under of copper container and then lit.
4. The water is stirred constantly with the thermometer until the temperature rises by, say, 30 oC
5. The flame is extinguished and the maximum temperature of the water is measured and recorded.
6. The burner and the remaining ethanol is reweighed. For example:
Mass of water (g)Initial temp of water (oC)Maximum temp of water (oC)Temperature rise (oC)Initial mass of spirit burner + ethanol (g)Final mass of spirit burner + ethanol (g)Mass of ethanol burnt (g)
10024.254.230.034.4633.680.78

The amount of energy produced per gram of ethanol burnt can also be calculated:

## 3:03 calculate the heat energy change from a measured temperature change using the expression Q = mcΔT

Calorimetry allows for the measurement of the amount of energy transferred in a chemical reaction to be calculated.

EXPERIMENT1: Displacement, dissolving and neutralisation reactions

Example: magnesium displacing copper from copper(II) sulfate

Method:

1. 50 cm3 of copper(II) sulfate is measured and transferred into a polystyrene cup.
2. The initial temperature of the copper sulfate solution is measured and recorded.
3. Magnesium is added and the maximum temperature is measured and recorded.
4. The temperature rise is then calculated. For example:
Initial temp. of solution (oC)Maximium temp. of solution (oC)Temperature rise (oC)
24.256.732.5

Note:  mass of 50 cm3 of solution is 50 g

EXPERIMENT2: Combustion reactions

To measure the amount of energy produced when a fuel is burnt, the fuel is burnt and the flame is used to heat up some water in a copper container

Example: ethanol is burnt in a small spirit burner

Method:

1. The initial mass of the ethanol and spirit burner is measured and recorded.
2. 100cm3 of water is transferred into a copper container and the initial temperature is measured and recorded.
3. The burner is placed under of copper container and then lit.
4. The water is stirred constantly with the thermometer until the temperature rises by, say, 30 oC
5. The flame is extinguished and the maximum temperature of the water is measured and recorded.
6. The burner and the remaining ethanol is reweighed. For example:
Mass of water (g)Initial temp of water (oC)Maximum temp of water (oC)Temperature rise (oC)Initial mass of spirit burner + ethanol (g)Final mass of spirit burner + ethanol (g)Mass of ethanol burnt (g)
10024.254.230.034.4633.680.78

The amount of energy produced per gram of ethanol burnt can also be calculated:

## 3:08 practical: investigate temperature changes accompanying some of the following types of change: salts dissolving in water, neutralisation reactions, displacement reactions and combustion reactions

Calorimetry allows for the measurement of the amount of energy transferred in a chemical reaction to be calculated.

EXPERIMENT1: Displacement, dissolving and neutralisation reactions

Example: magnesium displacing copper from copper(II) sulfate

Method:

1. 50 cm3 of copper(II) sulfate is measured and transferred into a polystyrene cup.
2. The initial temperature of the copper sulfate solution is measured and recorded.
3. Magnesium is added and the maximum temperature is measured and recorded.
4. The temperature rise is then calculated. For example:
Initial temp. of solution (oC)Maximium temp. of solution (oC)Temperature rise (oC)
24.256.732.5

Note:  mass of 50 cm3 of solution is 50 g

EXPERIMENT2: Combustion reactions

To measure the amount of energy produced when a fuel is burnt, the fuel is burnt and the flame is used to heat up some water in a copper container

Example: ethanol is burnt in a small spirit burner

Method:

1. The initial mass of the ethanol and spirit burner is measured and recorded.
2. 100cm3 of water is transferred into a copper container and the initial temperature is measured and recorded.
3. The burner is placed under of copper container and then lit.
4. The water is stirred constantly with the thermometer until the temperature rises by, say, 30 oC
5. The flame is extinguished and the maximum temperature of the water is measured and recorded.
6. The burner and the remaining ethanol is reweighed. For example:
Mass of water (g)Initial temp of water (oC)Maximum temp of water (oC)Temperature rise (oC)Initial mass of spirit burner + ethanol (g)Final mass of spirit burner + ethanol (g)Mass of ethanol burnt (g)
10024.254.230.034.4633.680.78

The amount of energy produced per gram of ethanol burnt can also be calculated:

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Section 1: Principles of chemistry

a) States of matter

b) Atoms

c) Atomic structure

d) Relative formula masses and molar volumes of gases

e) Chemical formulae and chemical equations

f) Ionic compounds

g) Covalent substances

h) Metallic crystals

i) Electrolysis

Section 2: Chemistry of the elements

a) The Periodic Table

b) Group 1 elements: lithium, sodium and potassium

c) Group 7 elements: chlorine, bromine and iodine

d) Oxygen and oxides

e) Hydrogen and water

f) Reactivity series

g) Tests for ions and gases

Section 3: Organic chemistry

a) Introduction

b) Alkanes

c) Alkenes

d) Ethanol

Section 4: Physical chemistry

a) Acids, alkalis and salts

b) Energetics

c) Rates of reaction

d) Equilibria

Section 5: Chemistry in industry

a) Extraction and uses of metals

b) Crude oil

c) Synthetic polymers

d) The industrial manufacture of chemicals

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