4.3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations Flashcards
What is the Law of Conservation of Mass?
The Law of Conservation of Mass states that no atoms are lost or made during a chemical reaction, so the mass of the products equals the mass of the reactants.
How are chemical reactions represented in symbol equations?
Chemical reactions are represented by symbol equations, which must be balanced in terms of the number of atoms of each element on both sides of the equation.
What is the purpose of multipliers in chemical equations?
Multipliers in equations serve two purposes: Before a formula (normal script) to indicate the number of molecules or ions. In subscript within a formula to show the number of atoms of each element in a compound.
What is the relative formula mass (Mr) of a compound?
The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the quantities shown in the formula.
How is the relative formula mass used in balanced chemical equations?
In a balanced chemical equation, the sum of the relative formula masses of the reactants equals the sum of the relative formula masses of the products.
How can you calculate the percentage by mass of an element in a compound?
The percentage by mass of an element in a compound can be calculated using the relative formula mass of the compound and the relative atomic masses of the elements.
Why might mass changes occur when a reactant or product is a gas?
Some reactions may appear to involve a change in mass, but this can often be explained by the involvement of gases in the reaction.
For example, when a metal reacts with oxygen, the mass of the oxide produced is greater than the mass of the metal. In the thermal decomposition of metal carbonates, carbon dioxide is released into the atmosphere, leaving the metal oxide as the only solid product.
How can mass changes be explained using the particle model?
In non-enclosed systems, mass changes during a chemical reaction can be explained in terms of the particle model, which shows how gases may escape or be absorbed, resulting in observable changes in mass.
What is the uncertainty in chemical measurements?
Uncertainty in chemical measurements refers to the fact that there is always some level of doubt or variation in the result obtained from any measurement.
How is uncertainty represented in measurements?
The distribution of results can be used to represent uncertainty. The range of a set of measurements around the mean can be used as a measure of uncertainty to determine how precise and reliable the measurements are.
