Free WACE Chemistry Flashcard Review

The particles need sufficient energy to overcome the activation-energy barrier and an orientation that allows the required bonds to change. A collision is not automatically a reaction. Raising concentration increases collision opportunities; it does not by itself make every collision sufficiently energetic or correctly oriented.

Powder exposes more solid surface to the other reactant, increasing collisions at the interface. The activation energy and amount of solid are unchanged. If the same amount reacts completely with another reagent in excess, the theoretical final product amount is unchanged even though the initial rate is larger.

More reactant particles occupy each unit volume, usually increasing the frequency of collisions between relevant species. The explanation must identify the reacting particles rather than merely say they are closer. Concentration does not directly change the activation-energy barrier or the equilibrium constant at fixed temperature.

Particles have a higher average kinetic energy, and a larger fraction can meet or exceed the activation energy. This increase in the energetic fraction is central to the faster reaction. The activation energy of a specified uncatalysed pathway is not lowered simply by warming the mixture.

At constant temperature, reducing volume increases reacting gas concentrations and partial pressures, making collisions more frequent. This explanation applies to reacting gases. Adding an inert gas at fixed volume raises total pressure without increasing the concentrations of the reacting species.

A catalyst provides an alternative pathway with a lower activation-energy barrier. It does not change the energies of the initial reactants or final products, so the enthalpy change is unchanged. It accelerates forward and reverse processes rather than altering the equilibrium composition at a fixed temperature.

Use the gradient of the tangent near the start, expressed as change in gas volume divided by change in time. A chord across a long interval gives an average rate instead. A steep initial slope and a large final volume describe different features: speed and total amount produced.

It establishes that no further measurable product volume is accumulating under those conditions. A limiting reactant may be exhausted or a reversible system may have reached equilibrium. The horizontal curve alone does not identify the mechanism, prove all reactants are gone, or show that molecular reactions have stopped.

Keep the solid material, mass and purity, solution concentration and volume, temperature, mixing and measurement method consistent. Change particle size deliberately and measure an initial rate or a clearly defined reaction time. Equal masses alone do not control the acid concentration or temperature.

Repeats help estimate random variation and can make an average less sensitive to random fluctuations. A consistently miscalibrated instrument shifts all results in a similar direction, so averaging preserves that systematic bias. Check against a suitable reference or recalibrate to address the cause.

A closed system exchanges energy but not matter with its surroundings. An isolated system exchanges neither. A sealed flask in a water bath is closed even though heat can pass through its walls. Calling it isolated simply because the stopper prevents gas escape confuses matter exchange with energy exchange.

Forward and reverse reactions continue at equal non-zero rates, leaving the macroscopic composition constant under unchanged conditions. This requires a system capable of retaining the relevant matter. Equal rates do not require equal reactant and product concentrations, and constant colour does not imply microscopic inactivity.

Yes. In a sealed container holding liquid water and water vapour at constant temperature, evaporation and condensation can occur at equal rates. Both phases persist while the amounts remain constant. No new chemical substance is needed for this example of a dynamic physical equilibrium.

Particles are consumed and regenerated at matching rates. Over a given time interval, the amount entering a species population equals the amount leaving it. Individual particles can change identity even while the total concentration stays constant; labelled-particle tracing can reveal that ongoing exchange.

The forward process can begin while the reverse rate is initially negligible because little or no product is available. As product accumulates, the reverse rate increases. Equilibrium is approached when the two rates become equal, rather than when all reactants disappear or both rates necessarily become zero.

Yes. For a reversible system, products can react in the reverse direction and establish a mixture containing reactants. Under the same temperature and compatible overall composition constraints, the resulting equilibrium obeys the same equilibrium constant. The direction of preparation does not create a different K.

It describes the relative abundance of products and reactants at equilibrium. A product-favoured position does not mean the forward reaction is faster at equilibrium; the two rates must still match. Position also does not measure how quickly equilibrium is reached, which depends on kinetic factors.

Escape continuously removes one species, so the matter balance differs from that of a sealed system. Further forward reaction may replace the escaping product. Constant observations in a continuously supplied or vented system may reflect a steady state rather than the closed-system dynamic equilibrium being modelled.

Look for stable macroscopic quantities under controlled conditions together with evidence of reversibility or continued two-way exchange. A catalyst or tracer experiment can probe the process without treating a stationary appearance as proof that nothing occurs. Colour alone may also stop changing when a reactant is exhausted.

The forward and reverse rate curves meet and then remain equal under unchanged conditions. They need not meet at zero. A concentration–time graph instead shows each concentration becoming constant; its separate plateaus need not have the same height. Do not transfer the equal-rate condition to concentration values.