Question

question 1
1 pts
in a chemical reaction
there are equal numbers of molecules on each side of the reaction arrow.
the number of atoms present in a reaction can vary when the conditions change during
the reaction.
there are always the same number of products as there are reactants.
there are equal numbers of atoms on each side of the reaction arrow.
question 2
1 pts
the scientific principle which is the basis for balancing chemical equations
is
the law of conservation of mass.
the law of definite proportions.
the law of conservation of energy.
avogadros law.
the law of conservation of mass and energy.

Explanation:

Question 1

• According to the law of conservation of mass in chemical reactions, atoms are neither created nor destroyed. So, the number of atoms of each element on the reactant side must equal the number on the product side.
• Molecules can combine or break apart in different ratios, so the number of molecules on each side of the reaction arrow is not necessarily equal.
• Atoms are conserved in a chemical reaction (conditions like temperature, pressure do not change the number of atoms in a chemical reaction as atoms are just rearranged).
• The number of products and reactants (in terms of the count of substances) can vary. For example, \(2H_2 + O_2

ightarrow2H_2O\), there are 2 reactant substances and 1 product substance.

• The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. When balancing chemical equations, we ensure that the mass of the reactants (since mass is related to the number of atoms of each element) is equal to the mass of the products. This is done by making sure that the number of atoms of each element is the same on both sides of the equation.
• The law of definite proportions states that a given chemical compound always contains its component elements in fixed ratio (by mass) and does not depend on its source or method of preparation. It is not directly about balancing equations.
• The law of conservation of energy is about energy changes (e.g., in thermochemical reactions) and not about the atom - count based balancing of chemical equations.
• Avogadro's law states that equal volumes of gases, at the same temperature and pressure, have the same number of molecules. It is more relevant for gas - volume relationships in reactions rather than general equation balancing.
• While the law of conservation of mass and energy (in the form \(E = mc^{2}\)) is a more comprehensive law in physics (especially in nuclear reactions), for general chemical reactions (where \(E=mc^{2}\) effects are negligible), the basis of balancing chemical equations is mainly the law of conservation of mass.

Answer:

the number of atoms on each side of the reaction arrow.

Question 2