Sec 4 Combined Science (Chemistry) Speed of Reactions topical questions

State, in terms of particles, the two conditions needed for a reaction to occur.

State the effect on the rate of reaction of: (a) increasing the temperature; (b) using powdered solid instead of one lump.

A gas syringe collects 48 cm³ of gas in 30 seconds. Calculate the mean rate of gas production in cm³/s.

Explain why increasing the pressure speeds up a reaction between two gases, but increasing the pressure on a liquid mixture has almost no effect.

Define the mean rate of a reaction, and state its units when gas volume is measured in cm³ and time in seconds.

For each change, state whether the rate increases or decreases, and name the factor responsible: (a) chilling a reacting mixture from 30 °C to 10 °C; (b) grinding a solid reactant into powder; (c) diluting an acid with extra water.

Explain, using collision theory, why increasing the concentration of hydrochloric acid increases its rate of reaction with magnesium.

A student investigates marble chips with acid at 20 °C and at 40 °C, collecting gas with identical syringes. State two variables that must be kept the same, and predict, with a collision-theory reason, how the 40 °C result differs.

The table shows gas volume against time for excess acid reacting with calcium carbonate: Time / s: 0, 20, 40, 60, 80 Volume / cm³: 0, 40, 64, 72, 72 (a) Calculate the mean rate over the first 20 seconds. (b) State when the reaction finished and how you know. (c) Explain why the rate was fastest at the start.

Explain why a fire burns much more fiercely in a draught of moving air than in still air, using the ideas of this chapter.

Magnesium reacts with excess dilute hydrochloric acid and the hydrogen is collected: Time / s: 0, 10, 20, 30, 40 Volume / cm³: 0, 22, 38, 46, 46 (a) Calculate the mean rate over the first 10 s. (b) Calculate the mean rate from 20 s to 30 s. (c) Explain why the two rates differ.

Explain each observation using collision theory: (a) a wooden splint glows in air but bursts into flame in a jar of pure oxygen; (b) fine flour dust floating in a mill can explode violently, although a bag of flour in the same room does not burn.

Two runs of excess acid + the same mass of powdered marble are compared. Run A: 1.0 mol/dm³ acid. Run B: 2.0 mol/dm³ acid, same volume and temperature. Run B's curve is steeper and flattens at 72 cm³ after 55 s; run A flattens at 72 cm³ after 110 s. (a) State which run was faster and how the data shows it. (b) Explain the difference with collision theory. (c) Explain why both runs flattened at the same volume.

A student compare three marble-chip samples — one lump, small chips, powder — each 2.0 g, each with 50 cm³ of the same excess acid at 25 °C. Times to collect 20 cm³ of gas: lump 240 s, small chips 90 s, powder 35 s. (a) State the variable deliberately changed and three variables controlled. (b) Explain the trend in the times using collision theory. (c) Predict, with a reason, the time for 2.0 g of the SAME powder at 40 °C.

A mass-loss experiment uses excess dilute hydrochloric acid with magnesium ribbon on a balance (cotton wool in the flask neck). The mass falls from 120.00 g to 119.04 g in 4 minutes, then stays constant. (a) Calculate the mean rate of mass loss in the first 4 minutes, in g/min. (b) What has the lost mass escaped as? Name the gas and write the equation for its formation. (c) State the shape of the mass–time graph between 0 and 4 minutes, and explain the shape.

An industrial process reacts two gases in a sealed chamber. An engineer can raise the temperature, raise the pressure, or both. Using collision theory, compare all three options for their effect on rate, and state one reason an engineer might raise the pressure rather than the temperature.

Two runs use 1.0 g of calcium carbonate with 50 cm³ of excess 1.0 mol/dm³ hydrochloric acid at 25 °C. Run P uses powdered marble and finishes in 40 s; run C uses large chips and finishes in 160 s. Both runs collect 48 cm³ of gas. (a) Compare the rates of the two runs, quoting the evidence. (b) Calculate the mean rate for run P. (c) A student claims: \u0027The powder made more gas because it reacted faster.\u0029 Use the data to correct this claim. (d) State what the 48 cm³ collected in each run actually depends on.

The same reaction is run at two temperatures; the total gas collected is 64 cm³ in both. Experiment 1 at 20 °C: 16 cm³ collected in the first 20 s; the reaction finishes at 200 s. Experiment 2 at 35 °C: 40 cm³ collected in the first 20 s; the reaction finishes at 70 s. (a) Calculate the mean rate over the first 20 s for each experiment. (b) How many times faster is the initial rate at 35 °C? (c) State and explain the effect of temperature on the time to completion. (d) Explain why both experiments collected the same total volume of gas.