As part of your GCSE chemistry studies, you’ll need to have a good understanding of why temperature changes occur during a chemical reaction. After all, a rise or fall in temperature is one of the important and measurable indicators of chemical change.
Conducting your own experiment is a great way to learn about the science behind temperature change in chemistry. In this article, we provide step-by-step instructions on how to produce a highly-exothermic (heat-releasing) chemical reaction between an acid and a base.
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What is a temperature change in chemistry?
In chemistry, temperature change occurs when chemical bonds are broken or created during a chemical reaction.
When two or more substances react, electrons are either shared equally among the atoms (covalent bonds) in the reactants or they’re transferred from one to another (ionic bonds). This process of sharing and transferring electrons disturbs the energy in the orbital shells.
Depending on the type of reactants, the electrons may either release or absorb energy. This will be in the form of heat and light.
The two main types of temperature change
Temperature change is an important and measurable indicator of chemical change.
As we’ve already explained, the atoms in the reactants may either release or absorb heat energy. The former is called an exothermic reaction, while the latter is known as an endothermic reaction.
1. Exothermic
During an exothermic reaction, heat energy is released into the system. A common example of an exothermic reaction is combustion, or burning.
In a combustion reaction, a fuel such as butane reacts with oxygen to produce carbon dioxide and water. If the reaction is incomplete, some carbon residue or soot is left behind.
2. Endothermic
Conversely, in an endothermic reaction, heat energy is absorbed from the system.
Photosynthesis is a good example of an endothermic reaction because the process absorbs more energy than it releases. As a result, the overall temperature of the system is reduced.
What is the chemical equation for temperature change?
A temperature change in a chemical reaction is expressed using this simple formula:
ΔT = Tf−Ti
Delta T in this reaction represents the change in temperature. This change is the difference between the temperature at the start of the reaction and the temperature at the end. It’s important to note that this concept relates to the specific heat of every substance.
The specific heat is the amount of energy that has to be transferred to or from a substance to change its temperature by one degree Celsius. It’s expressed in Joule per gram degree Celsius, or J/g°C.
What’s the objective of this experiment?
The main objective of this experiment is to demonstrate the change in temperature during a chemical reaction. It will focus on an exothermic reaction between an acid (in this case, hydrochloric acid) and a base (sodium hydroxide).
As you’ll discover, the heat produced during this neutralisation reaction is directly proportional to the strength and concentration of the reactants.
Equipment & tools needed
To perform this relatively simple experiment, you’ll need the following laboratory equipment and tools:
- Laboratory thermometer (digital or mercury)
- 100 mL graduated cylinder
- Two 50 mL beakers
- Triple beam balance or a digital weighing scale
- Sodium hydroxide powder
- Hydrochloric acid
- Distilled water
- Personal protective equipment such as goggles and gloves.
Once you’ve prepared your equipment, follow the steps below to perform the experiment.
Step 1: Pour 25 mL of sodium hydroxide into the measuring cylinder
You can either prepare a solution of sodium hydroxide of about 1M or you can use a ready-made solution from the lab. Measure a 25 mL solution of sodium hydroxide using a graduated cylinder and transfer it to a beaker.
Step 2: Measure the temperature of the liquid
Next, measure the temperature of the solution and record it as the initial temperature. This will serve as your baseline measurement.
If you’re using a standard prepared solution, this measurement is likely to be around room temperature. However, if the solution has been freshly mixed, the temperature may be higher than the room or ambient temperature.
Step 3: Pour 5 mL of hydrochloric acid into the same cylinder
Using the same graduated cylinder, measure 5 mL of hydrochloric acid. As when handling any kind of acid or hazardous substance, always wear the appropriate PPE to prevent injuries.
Step 4: Mix the liquids together
Pour the hydrochloric acid solution into the 25 mL sodium hydroxide solution. As you do this, the temperature will increase. The heat produced is due to the neutralisation reaction between the acid and the base.
Step 5: Record the maximum temperature the liquids reach
The next step is to start recording the temperature change. To do this, immerse the probe portion of the thermometer into the solution.
Wait until the temperature becomes the same as the ambient temperature. Make sure you take note of the maximum temperature it reaches before it subsides.
Step 6: Repeat steps 1 to 5, increasing the hydrochloric acid by 5 mL each time
You’ll need to repeat the above process at least five more times until the volume of the mixed solution reaches 50 mL.
Take note of the change in temperature as you continue to add the hydrochloric acid solution. If the two solutions have a concentration of 1 M, the complete neutralisation point will be at 50 mL.
Both reactants need to be at 1 M or equal mole value to completely react with each other, producing water and salt. The balanced chemical equation can be written as:
HCl + NaOH → NaCl + H2O
Summary
A temperature change occurs when chemical bonds are broken or formed in a chemical reaction. During this process, heat energy is either released (an exothermic reaction) or absorbed (an endothermic reaction). You can measure temperature change by conducting a simple neutralisation experiment using an acid and a base.
