To determine which of the given statements about chemical reactions is true, let's analyze each statement with respect to the chemical reaction [tex]\( \text{HCl} + \text{KOH} \rightarrow \text{KCl} + \text{H}_2\text{O} \)[/tex] and general principles of chemistry.
1. Atoms are neither created nor destroyed during a chemical reaction.
This statement is true. According to the law of conservation of mass, atoms are conserved in a chemical reaction. They are simply rearranged to form new substances. In the reaction [tex]\( \text{HCl} + \text{KOH} \rightarrow \text{KCl} + \text{H}_2\text{O} \)[/tex], all the atoms from the reactants (H, Cl, K, O) are present in the products. No atoms are created or destroyed; they are just rearranged to form new compounds.
2. Chemical reactions always require heat to begin.
This statement is not necessarily true. While some chemical reactions do need an input of heat (endothermic reactions), others can occur at room temperature or even release heat themselves (exothermic reactions). Many reactions can be initiated without the need for external heating, such as reactions catalyzed by enzymes in biological systems.
3. All chemical reactions produce heat.
This statement is also not necessarily true. Not all chemical reactions produce heat. Reactions can be either exothermic (release heat) or endothermic (absorb heat). An endothermic reaction, for instance, requires heat energy from its surroundings to proceed, thus it does not produce heat but rather consumes it.
Based on our analysis, the true statement among the given options is:
Atoms are neither created nor destroyed during a chemical reaction. This aligns with the law of conservation of mass.
Therefore, the correct answer is:
[tex]\[ \boxed{1} \][/tex]
This is the true statement among the options provided.
