6.1 Practice problems

Correction to text p. 167 (Fig. 7)

The concentration of reactants & products changes over time Suggest a chemical equation that matches this data.

The concentration of reactants & products changes over time Suggest a chemical equation that matches this data. How do we write rate equations?

Coming soon… equilibrium systems (Topic 7)

Practice problem 1 In the chemical reaction of calcium carbonate with hydrochloric acid, 52.0 cm3 of carbon dioxide was generated in 60.0 s. Calculate the average rate in cm3 s-1. Write the balanced chemical equation including state symbols. Calculate the moles AND grams of carbon dioxide generated in 60.0 s; assume STP. From pH measurements, it was determined that the hydrochloric acid concentration was initially 0.0750 mol/L and was 0.0292 mol/L at t = 60.0 s. Calculate the average rate in mol dm-3 s-1.

The graph shows how the volume of carbon dioxide formed changes over time when a hydrochloric solution is added in excess to calcium carbonate in a flask. Explain the shape of the graph Copy the graph and sketch the curve you would obtain if the volume of hydrochloric acid solution were doubled and the concentration of the solution were halved (everything else is kept the same). Outline one other way in which the rate of this reaction can be studied in a school lab. Define the term activation energy and give one reason why the reaction between calcium carbonate and hydrochloric acid takes place at a reasonably fast rate at room temperature. V[Co2] Time

The data in the table was recorded for the decomposition of hydrogen peroxide using a manganese(IV) oxide catalyst. The total volume of oxygen gas collected was measured at different times. Deduce the balanced chemical equation for the reaction including state symbols. Draw a graph of the total volume of oxygen vs. time Calculate the average rate in cm3 min-1 correct to one decimal. Deduce in s how long it took for 40 cm3 of oxygen to be collected Determine the initial rate in cm3 min-1 Determine the instantaneous rate at t = 4 min Explain whether the catalyst used is heterogeneous or homogenous Time/ min 1 2 3 4 5 6 7 8 9 10 V of O2/ cm3 18 32 42 50 56 61 64

A series of experiments was carried out to measure the volume of gas produced when magnesium reacts with dilute hydrochloric acid. The equation for the reaction is: Mg + 2HCl  MgCl2 +H2 In the first experiment, 0.10 g of Mg ribbon was reacted with 30 cm3 of 0.50 mol dm-3 HCl. The data for this experiment are recorded in the table. The reaction was carried out at 20°C. Draw a graph of the data and explain in terms of collision theory, how the rate changes over time. Use the graph to calculate the initial rate of the reaction with units Time/s 15 30 45 60 75 90 105 120 135 150 165 180 Volume of gas/cm3 18.6 32.3 44.3 54.8 62.7 68.4 72.6 74.9 75.4 75.6

A series of experiments was carried out to measure the volume of gas produced when magnesium reacts with dilute hydrochloric acid. The equation for the reaction is: Mg + 2HCl  MgCl2 +H2 In the first experiment, 0.10 g of Mg ribbon was reacted with 30cm3 of 0.50 mol dm-3 HCl. The data for this experiment are recorded in the table. The reaction was carried out at 20°C. Draw a graph of the data and explain in terms of collision theory, how the rate changes over time. Use the graph to calculate the initial rate of the reaction with units Calculate the average rate for the first 120 mins. Now consider that 0.10g of powder Mg was used instead. Sketch a new graph on your graph labeled X to show how this reaction would compare. Now the consider if the experiment took place at 10°C. Sketch what this graph would look like and label this graph Z. Sketch the Maxwell-Boltzmann for the first reaction and the one in step 5 and use this to explain the effect of a temperature change on the rate of the reaction.