Biology: Thermodynamics and H+ Ions Essay

Submitted By busterboy1
Words: 928
Pages: 4

Investigating how much energy is transferred as heat when acids react with alkalis
Investigating how much energy is transferred as heat when acids react with alkalis

Hypothesis
The amount of heat transferred differ when altering the volume of acid in a neutralization reaction between acids and alkalis. The amount of heat transferred differ when altering the concentration of acids and alkalis in a neutralization reaction between acid and alkali.
Acid and Alkalis
Acids
Acids are substances that have a pH that is below 7 and turns the universal indicator yellow, orange or red. They form solutions containing hydrogen ions (H+). When you dissolve hydrogen chloride in water it releases H+ ions and cl- ions.
HCl H+ + Cl-
When ethonic acid dissolves in water it releases H+ ions and CH3 Coo-
CH3CooH H+ + CH3 Coo-
When acids release H+ ions, we call them H+ donors. A H+ ion is a hydrogen atom that has lost its single electron. This leaves a lone, positively charged proton. Because acids donate protons, they are sometimes also called proton donors.
Alkalis
Alkalis are substances that have a pH that is above 7 and they turn the universal indicator blue or purple. They form solutions containing hydroxide ions (OH-). Sodium hydroxide is a strong alkali whilst ammonia is a week alkali. When ammonia is dissolved in water, it forms ammonium hydroxide (NH + OH).
Bases
All alkalis are bases. Bases are substances that react with acids by absorbing hydrogen ions. The oxides, hydroxides and carbonates of metals such as sodium hydroxide, are bases. Some bases are soluble in water, these are called alkalis. All alkalis contain hydroxide ions (OH-). The more OH- ions in the solution the stronger the alkali.
Neutralization Reactions
In a neutralization reaction, an acid reacts with an alkali to produce a salt and water. When an acid reacts with the alkali the acids H+ ions react with the alkalis OH- ions forming
H+ + OH- H2O
This process takes place in all neutralization reaction.
An example would be:
Hydrochloric acid + Sodium hydroxide Sodium Chloride + Water
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
Energy Changes
Exothermic Reactions
Exothermic reaction release thermal energy into their surroundings. Exothermic reaction can occur spontaneously and some are explosive. During an exothermic reaction, chemical energy in the reactants is converted to thermal energy. This causes the temperature of the reaction to rise. The thermal energy created in the reaction is eventually lost to the surroundings and the temperature of the reaction mixture returns to normal.
The energy transfer in an exothermic reaction can be represented in an energy level diagram.
Reactants
Reactants

Energy (KJ)
Energy (KJ)

-ve
-ve

Products
Products

Reaction (time)
Reaction (time)

Endothermic Reactions
Endothermic reactions absorb thermal energy and can cause a decrease in temperature to the surroundings, During an endothermic reaction thermal energy from the reaction mixture is converted to chemical energy in the products this causes the temperature of the reaction mixture to fall. The thermal energy from the surroundings is transferred to the reaction mixture.

Energy (KJ)
Energy (KJ)
Products
Products
The energy transfer in an endothermic reaction can be represented in an energy level diagram.
+ve
+ve

Reaction (time)
Reaction (time)
Reactants
Reactants

Enthalpy Calculations
Enthalpy change can be calculated using the following equation: q=mc delta T.
Q= enthalpy change in joules.
M= mass of substance being heated (often water) in grams.
C= specific heat capacity in joules per kelvin per gram (4.18JK-1g-1 for water).
Delta T= change of temperature in…