The best examples of endothermic reactions: 3 practical examples you actually see in real life

Most students meet endothermic reactions in a diagram: a beaker, a thermometer, and an arrow labeled “energy in.” That’s fine for a test, but it’s not how your brain remembers things. Your brain remembers real examples.

So before we talk equations, let’s start with three practical examples of endothermic reactions that matter in everyday life, industry, and even global climate.

Example 1: Instant cold packs – the classic “feel it in your hand” endothermic reaction

If you’ve ever sprained an ankle in gym class and grabbed one of those squeeze-to-activate cold packs, you’ve literally held an endothermic reaction.

Inside a typical disposable cold pack, there are two compartments:

• One contains water.
• The other contains a solid, often ammonium nitrate (NH₄NO₃) or urea (CO(NH₂)₂).

When you squeeze the pack, the inner barrier breaks. The solid dissolves in the water, and that dissolution process absorbs heat from the surroundings—mainly from your skin. The temperature of the pack can drop by 20–30 °F within a minute or two, depending on the formulation.

Chemically, for ammonium nitrate, you can write the process like this:

\[ \text{NH}_4\text{NO}_3 (s) \rightarrow \text{NH}_4^+ (aq) + \text{NO}_3^- (aq) \]

The enthalpy change (ΔH) for dissolving ammonium nitrate in water is positive, meaning heat is absorbed from the surroundings. That’s the thermochemistry definition of an endothermic reaction.

Why does this matter beyond first aid?

• It’s a controlled, portable heat-absorbing system, useful in sports medicine.
• It’s a clean example teachers use in labs to show how temperature drops when enthalpy increases in the system.

This is often one of the best examples of endothermic reactions: 3 practical examples you’ll see in any chemistry class, because you can literally feel the energy transfer.

Other dissolution reactions that are endothermic include:

• Potassium chloride (KCl) dissolving in water
• Ammonium chloride (NH₄Cl) dissolving in water

Not every salt dissolving in water is endothermic (some are exothermic), which makes these examples of endothermic reactions especially useful for comparing behaviors.

Example 2: Photosynthesis – the planet-scale endothermic reaction

On the other end of the spectrum from cold packs, we have photosynthesis, one of the most important real examples of endothermic reactions on Earth.

The simplified reaction for photosynthesis is:

[
6\text{CO}_2 (g) + 6\text{H}_2\text{O} (l) + \text{energy (sunlight)} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 (aq) + 6\text{O}_2 (g)
]

Plants, algae, and some bacteria absorb energy from sunlight and use it to convert carbon dioxide and water into glucose and oxygen. In thermochemical terms, this process has a positive ΔH—it absorbs energy. That makes photosynthesis an endothermic reaction.

Why this is one of the best examples of endothermic reactions:

• It literally stores solar energy in chemical bonds.
• It underpins the global food chain and oxygen production.
• It’s central to discussions about climate change and carbon cycles.

According to the U.S. National Oceanic and Atmospheric Administration (NOAA), photosynthesis in the oceans alone is responsible for a large fraction of the world’s oxygen production and carbon uptake, tying a textbook thermochemistry idea directly to climate models and global policy.

From a learning standpoint, photosynthesis is a powerful example of an endothermic reaction because it shows that “heat” in chemistry doesn’t always mean a flame or a hot beaker. Here, the energy source is light, but in thermodynamic terms, it still counts as energy absorbed by the system.

Example 3: Cooking and baking – everyday endothermic reactions in your kitchen

Walk into a kitchen, and you’re surrounded by examples of endothermic reactions: 3 practical examples might not be enough to cover them all.

When you bake a cake, cook an egg, or toast bread, you’re driving chemical changes that require energy input. The food absorbs heat from the oven, stove, or toaster, and that energy goes into:

• Breaking and rearranging chemical bonds
• Denaturing proteins
• Driving off water (evaporation)

These processes are not just physical warming; they involve endothermic chemical changes.

For instance:

• Baking bread involves endothermic reactions in the dough as proteins and starches reorganize and as baking powder or yeast generate gas.
• Cooking an egg involves denaturation and coagulation of proteins, which require energy input.

The system (your food) absorbs heat and undergoes chemical change. From a thermochemistry perspective, many of these transformations have positive enthalpy changes and won’t proceed without constant heat input.

This is one of the most relatable real examples of endothermic reactions because everyone has watched raw ingredients transform into something completely different thanks to heat.

More real-life examples of endothermic reactions and processes

To strengthen your intuition, it helps to see more than just 3 practical examples. Here are additional real examples where energy is absorbed from the surroundings.

Melting ice and snow

When ice melts at 32 °F (0 °C), it absorbs heat from its surroundings to break the hydrogen bonds in the solid structure. The temperature of the ice–water mixture stays at 32 °F during melting, but heat is still flowing in. That heat is used as latent heat of fusion.

Process:

\[ \text{H}_2\text{O} (s) \rightarrow \text{H}_2\text{O} (l) \]

This is an endothermic process. It’s not a chemical reaction (no new substances), but in thermochemistry we still treat it as a heat-absorbing transformation. On a larger scale, the melting of polar ice is a major energy sink in Earth’s climate system.

Evaporation of sweat – your built-in endothermic cooling system

When you sweat, your body is counting on an endothermic phase change to keep you alive in hot conditions. As sweat evaporates from your skin, it absorbs heat from your body.

Process:

\[ \text{H}_2\text{O} (l) \rightarrow \text{H}_2\text{O} (g) \]

The U.S. Centers for Disease Control and Prevention (CDC) notes that evaporation is a key mechanism in how the body cools itself during heat exposure. Thermodynamically, this is an endothermic process: the water molecules need energy to escape the liquid phase, and they take that energy from your skin, lowering your body’s surface temperature.

Again, it’s not a chemical reaction, but it is one of the most important examples of endothermic processes in human physiology.

Dissolving ammonium nitrate, ammonium chloride, and urea in water

We already met ammonium nitrate in cold packs, but it’s worth highlighting a few salts whose dissolution in water is strongly endothermic:

• Ammonium nitrate (NH₄NO₃) – used in instant cold packs and some fertilizers
• Ammonium chloride (NH₄Cl) – used in some cooling demonstrations in the lab
• Urea (CO(NH₂)₂) – used in certain cold pack formulations and as a fertilizer

In each case, the enthalpy of solution (ΔH_solution) is positive. The solid dissolves only by absorbing heat from the water and surroundings. The result is a noticeable drop in temperature, which makes these great examples of endothermic reactions in classroom experiments.

Thermal decomposition reactions

Many decomposition reactions are endothermic because they require energy to break chemical bonds.

Two classic examples:

• Decomposition of calcium carbonate (limestone):

  \[ \text{CaCO}_3 (s) \rightarrow \text{CaO} (s) + \text{CO}_2 (g) \]

  This reaction is used in cement production. It requires high temperatures in kilns, meaning energy must be supplied continuously. The positive ΔH shows it’s endothermic.

• Decomposition of potassium chlorate (KClO₃) in older lab demonstrations to produce oxygen:

  \[ 2\text{KClO}_3 (s) \rightarrow 2\text{KCl} (s) + 3\text{O}_2 (g) \]

  Again, heat input is necessary to sustain the reaction.

These are strong examples of endothermic reactions in industrial and laboratory contexts, showing that endothermic behavior is not just a classroom curiosity.

Connecting endothermic reactions to enthalpy (ΔH) and temperature

To really master examples of endothermic reactions: 3 practical examples and beyond, you need to connect the everyday experiences to the thermochemistry language.

Key ideas:

• Endothermic reaction: A chemical reaction (or process) with ΔH > 0. The system absorbs heat from the surroundings.
• Temperature drop: In many experiments, the temperature of the surroundings (like the solution in a beaker) decreases as heat flows into the reaction.
• Energy source: The energy can come from heat, light (as in photosynthesis), or sometimes electricity.

In a simple calorimetry setup, if you measure the temperature change when a salt dissolves in water, you can calculate the enthalpy change using:

\[ q = m c \Delta T \]

where:

• \( q \) is heat absorbed or released
• \( m \) is mass of the solution
• \( c \) is specific heat capacity
• \( \Delta T \) is the temperature change

For an endothermic reaction, \( q \) for the system is positive, and \( \Delta T \) of the surroundings is often negative (temperature falls). This ties the real examples of endothermic reactions—like your cold pack or dissolving ammonium nitrate—directly to measured data.

If you’re studying for exams, anchor the concept in your mind with this pattern:

• Cold pack gets cold → reaction absorbs heat → endothermic → ΔH > 0.
• Oven stays hot while food changes → food absorbs heat → many cooking reactions are endothermic.
• Plant absorbs sunlight → builds glucose → endothermic photosynthesis.

These examples of endothermic reactions are not just trivia; they are shortcuts to remembering how enthalpy and temperature relate.

Why these 3 practical examples are so widely used in teaching

Teachers and textbooks keep coming back to instant cold packs, photosynthesis, and cooking as the best examples of endothermic reactions: 3 practical examples for a reason:

• Sensory impact: You can feel a cold pack, see a plant grow, and taste cooked food.
• Scales of energy: From a small pouch in your hand to the entire biosphere, you see how endothermic processes operate at different scales.
• Data-friendly: These examples are easy to measure in school labs—temperature changes, light intensity, reaction times.

If you’re building a study guide or teaching plan, these three, plus melting ice, evaporating sweat, and dissolving specific salts, give you a solid set of real examples of endothermic reactions that students can connect to quickly.

FAQ: common questions about examples of endothermic reactions

What are some everyday examples of endothermic reactions?

Everyday examples of endothermic reactions include instant cold packs, photosynthesis in plants, and many cooking and baking processes. You also see endothermic behavior in melting ice, evaporating sweat, and dissolving certain salts like ammonium nitrate in water.

Is melting ice an example of an endothermic process or reaction?

Melting ice is an endothermic process, not a chemical reaction. The substance (water) stays the same, but it absorbs heat to change from solid to liquid. It’s still a great example of an endothermic change when learning thermochemistry.

Is photosynthesis an example of an endothermic reaction?

Yes. Photosynthesis is a classic example of an endothermic reaction because plants absorb energy from sunlight to convert carbon dioxide and water into glucose and oxygen. The overall enthalpy change is positive, meaning energy is stored in the products.

Are all dissolving processes examples of endothermic reactions?

No. Some dissolving processes are endothermic, and some are exothermic. For instance, dissolving ammonium nitrate in water is an example of an endothermic reaction (temperature drops), while dissolving calcium chloride releases heat (temperature rises), making it exothermic.

How can I quickly recognize an example of an endothermic reaction in an experiment?

Look for a temperature decrease in the surroundings (like the solution or container) while the reaction proceeds, or for continuous energy input (heat or light) being required to keep the reaction going. If the system absorbs energy and has a positive ΔH, you’re looking at an endothermic reaction.

If you remember nothing else, remember this: when you hear “endothermic,” think of cold packs, sunlight in plants, and heat in your oven. Those three anchor points will help you recognize and explain many other examples of endothermic reactions: 3 practical examples and beyond, from classroom experiments to planetary climate systems.