chemistry C3 Flashcards
(40 cards)
Q: What is the law of conservation of mass?
A: The law of conservation of mass states that no atoms are lost or made in a chemical reaction. Therefore, no mass is lost or made.
Q: What must be true about the mass of reactants and products in a chemical reaction according to the law of conservation of mass?
A: The mass of the products at the end of a reaction must equal the mass of the reactants at the start.
Q: How do you balance a symbol equation?
A: You balance a symbol equation by ensuring the same number of atoms of each element are present on both sides. You can add numbers in front of chemical formulae as multipliers, but never change the numbers within a formula.
Q: What is relative atomic mass (Ar)?
A: The relative atomic mass (Ar) of an element is its average atomic mass.
Q: How do you calculate the relative formula mass (Mr) of a compound?
A: The Mr of a compound is found by adding up the relative atomic masses (Ar) of all the atoms in the compound. For example, the Mr of CO2 is 12 (C) + 16×2 (O) = 44.
Q: What is the relationship between Ar and the mass number of an element?
A: The Ar of an element is the same as its mass number, which is shown in the periodic table.
Q: What happens in a non-enclosed system during a chemical reaction?
A: In a non-enclosed system, reactants from the environment can enter, and products, usually gases, can escape into the environment.
Q: Why might the mass of products seem greater than the mass of reactants in a non-enclosed system?
A: The mass of products may seem greater if one of the reactants is a gas from the air, like oxygen reacting with a metal. The mass of the oxygen is not initially included in the reactants but is part of the product (metal oxide).
Q: Why might the mass of products seem less than the mass of reactants?
A: The mass of products may seem less if one of the products is a gas that escapes into the environment, like carbon dioxide from the decomposition of a metal carbonate.
Q: What is uncertainty in an experiment?
A: Uncertainty is the possibility that the measurements made in an experiment could be wrong. It can be estimated using the range or by plotting results on a graph.
Q: What does a range bar on a graph represent?
A: A range bar on a graph shows the uncertainty by indicating the range of results. A longer range bar indicates a higher uncertainty.
Q: What is a mole in terms of particles?
A: A mole contains 6.02 × 10²³ particles, known as the Avogadro constant. This number is the same regardless of the type of particle.
Q: How is the mass of 1 mole of a substance related to its Mr?
A: The mass of 1 mole of a substance in grams is the same as its relative formula mass (Mr).
Q: How do you calculate the number of moles from mass?
A: To calculate the number of moles, divide the mass of the substance (in grams) by its relative formula mass (Mr).
Q: What is the limiting reactant in a chemical reaction?
A: The limiting reactant is the substance that is completely used up first, limiting the amount of products that can be formed.
Q: What are excess reactants?
A: Excess reactants are substances that remain after the limiting reactant has been completely used up in a chemical reaction.
Q: How is the maximum possible amount of product determined?
A: The maximum possible amount of product is determined by the amount of the limiting reactant.
Q: What is concentration in chemistry?
A: Concentration is a measure of how much solute is dissolved in a certain volume of solution.
Q: How is concentration measured?
A: Concentration can be measured in grams per dm³ (g/dm³) or moles per dm³ (mol/dm³).
Q: What is yield in a chemical reaction?
A: Yield is the amount of product that is produced in a reaction.
Q: What is the difference between actual yield and maximum theoretical yield?
A: The maximum theoretical yield is the maximum amount of product that could form, while the actual yield is the amount actually produced in the experiment.
Q: What is atom economy?
A: Atom economy is the measure of how much of the starting materials in a chemical reaction end up as useful products.
Q: Why are reactions with high atom economies preferred?
A: Reactions with high atom economies are preferred because they produce more useful products with fewer wasted materials, making them better for profits and the environment.
Q: What factors affect the choice of reaction for a product?
A: Factors include yield, equilibrium position, reaction rate, and the usefulness of by-products.
