Chem Flashcards
Q: Define the law of conservation of mass.
A: The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.
Q: What does the law of conservation of mass state?
A: Mass is conserved in chemical reactions, meaning it’s neither created nor destroyed. For example, when wood burns, the mass of the ash and gases produced equals the mass of the original wood and oxygen used.
Q: What occurs to atoms in a chemical reaction?
A: Atoms are rearranged to form new substances. For example, in the reaction between hydrogen and oxygen to form water, H₂ and O₂ molecules are rearranged to form H₂O molecules.
Q: What are some observable signs of a chemical reaction?
A: Common signs include color change, gas production, and temperature change. For example, mixing vinegar and baking soda produces bubbles, indicating gas formation.
Q: What are the pros of using balanced chemical equations?
A: They show the exact proportions of reactants and products. For example, balancing H₂ + O₂ → H₂O helps us see we need 2 H₂ molecules for every O₂ molecule to produce water.
Q: How can we count the number of atoms in a compound with a coefficient (e.g., 6H₂O)?
A: Multiply each atom by the coefficient. For example, in 6H₂O, there are 12 hydrogen atoms and 6 oxygen atoms.
Q: Why is sodium’s reactivity important in certain reactions?
A: Sodium is highly reactive, which can make it dangerous. For example, when exposed to water, sodium reacts violently, producing heat and hydrogen gas.
Q: What are some limitations of balanced chemical equations?
A: They don’t show intermediate steps or energy changes. For example, CH₄ + 2O₂ → CO₂ + 2H₂O doesn’t show the heat released in methane combustion.
Q: Why did early alchemists believe in creating new substances from existing ones?
A: They saw transformations (e.g., iron rusting) and thought they could create new elements, like gold, through similar processes.
Q: What might cause an object to increase in mass during a chemical reaction?
A: Oxygen or another element can combine with it. For example, iron gains mass when it rusts because it bonds with oxygen.
Q: Why might the mass decrease in an open system where gas is produced?
A: Gas escapes into the air. For example, when magnesium reacts with acid and produces hydrogen gas, the gas leaves, reducing the mass of the system.
Q: What happens to individual atoms in a substance during combustion?
A: They bond with oxygen to form new compounds. For example, carbon in fuel bonds with oxygen to form CO₂ during combustion.
Q: Why do specific amounts of products form from reactants in a chemical reaction?
A: It’s based on the atoms available in the reactants. For example, burning propane (C₃H₈) produces 3 CO₂ molecules because it has 3 carbon atoms.
Q: What is the role of reactants in a chemical reaction?
A: Reactants are substances that undergo change. For example, in the reaction H₂ + O₂ → H₂O, H₂ and O₂ are the reactants.
Q: What is combustion in chemical terms?
A: Combustion is a reaction with oxygen that releases heat. For example, burning wood is a combustion reaction that produces CO₂ and water vapor.
