As the cement sets and hardens, it generates heat. This is called:
🔥 The Source of Heat in Concrete
The hardening of cement is not a drying process but a chemical one. When water is mixed with cement, it triggers a series of chemical reactions with the cement compounds. This entire process is called hydration. A fundamental characteristic of this process is that it is exothermic, meaning it releases energy in the form of heat. This generated heat is a direct result of the chemical bonds being formed as the cement hydrates and turns into a hardened, stable material.
📝 Detailed Analysis of the Options
(b) Latent heat
This is incorrect. Latent heat is the energy absorbed or released during a change of state (like ice melting to water or water boiling to steam) *without* a change in temperature. The heat from cement is generated by a chemical reaction, not a phase change.
(c) Heat of vaporisation
This is incorrect. This is a specific type of latent heat—the heat required to turn a liquid into a gas. This is the opposite of what is happening in concrete, where water is being chemically bound, not evaporated.
(d) Sensible heat
This is incorrect. Sensible heat is the heat energy that causes a change in temperature of a substance but does not change its state. While the heat generated does cause a sensible heat change (the concrete gets hotter), the *name* for the heat generated by the reaction itself is not sensible heat.
(a) Heat of hydration
This is the correct answer. The specific term for the heat released during the chemical reaction between cement and water is the heat of hydration. It is a direct measure of the energy liberated as the cement compounds form new, stable hydrated products. This term accurately describes both the source of the heat (hydration) and its nature.
📊 Types of Heat in Thermodynamics
| Term | Definition | Relevance to Cement |
|---|---|---|
| Heat of Hydration | Heat released during a chemical reaction with water. | The correct term for heat generated by cement. |
| Latent Heat | Heat for phase change at constant temperature. | Not relevant to the primary heat generation. |
| Sensible Heat | Heat that causes a temperature change. | The temperature rise in concrete is a *result* of sensible heat, but not the name of the source heat. |
💡 Study Tips
- Link the Words: The process is called Hydration. The heat it produces is called the Heat of Hydration. The link is direct and easy to remember.
- It's a Chemical Reaction: Always remember that the heat comes from a chemical reaction, not from drying or a change of state. This helps eliminate options like latent heat or heat of vaporization.
- Exothermic is Key: Knowing that the reaction is exothermic (releases heat) immediately tells you that the concrete will get warmer, and this heat needs a specific name related to its chemical origin.