Subject
Chemistry study guides
Atoms, bonds, reactions, and the periodic table — with step-by-step reasoning and interactive tools.
7 explained questions, each with the answer, a worked explanation, and something interactive to help it stick.
- Which Symbol Can Be Used to Indicate the Pressure at Which a Chemical Reaction Is Carried Out?The unit "atm" (atmosphere) written above the reaction arrow indicates the pressure at which a reaction is carried out, for example "2 atm." Symbols such as Δ or a temperature like 25°C indicate heat, not pressure, so "atm" is the correct choice.Read the guide
- Which statement correctly describes a chemical reaction?The correct statement is that a chemical reaction rearranges atoms: existing bonds between atoms in the reactants break and new bonds form, turning reactants into chemically different products. Energy may be either absorbed or released, not always released.Read the guide
- What is the law of definite proportions?The law of definite proportions (also called the law of constant composition) states that a given chemical compound always contains the same elements in the same fixed ratio by mass, regardless of its source, size, or how it was made. Water, for example, is always about 11.2% hydrogen and 88.8% oxygen by mass.Read the guide
- Which of these is an example of a physical change?A physical change alters a substance's form or state without creating any new substance. Examples include melting ice, boiling or freezing water, dissolving sugar or salt, cutting paper, and crushing a can. Burning, rusting, and cooking are chemical changes because they form new substances.Read the guide
- Which statement best describes the amount of catalyst that remains at the end of a reaction?The amount of catalyst is the same at the end as at the beginning. A catalyst lowers a reaction's activation energy without being consumed — it is regenerated in the mechanism — so it emerges unchanged in both quantity and chemical identity.Read the guide
- How Is Energy Related to the Change of State Represented by the Model?During the change of state shown, particles gain energy: as a substance moves to a higher-energy state (such as solid to liquid to gas), it absorbs energy to overcome the attractions between particles. That endothermic transition means energy is taken in, not released.Read the guide
- The unequal sharing of electrons within a water molecule makes the water molecule _____.Polar. Oxygen is far more electronegative than hydrogen, so it pulls the shared bonding electrons closer to itself. This gives oxygen a partial negative charge and each hydrogen a partial positive charge, making the bent water molecule an electric dipole, that is, polar.Read the guide