IB Docs (2) Team MC test: Measuring energy changes
Multiple choice test on 5.1 Measuring energy changes
Use the following 'quiz' to test your knowledge and understanding of this sub-topic. You will need access to a periodic table (Section 6 of the IB data booklet).
If you get an answer wrong, read through the explanation carefully to learn from your mistakes.
Which is a correct statement about heat and temperature?
Heat is a form of energy but temperature is a measure of 'hotness', i.e. it represents the average kinetic energy of the particles. Heat and temperature are measured in completely different units. The specific heat capacity is the amount of energy it takes to heat 1 g of water by 1 oC (or 1 kg by 1 K) . It is measured in J g−1 oC−1 or kJ kg−1 K−1. The amount of heat that will be given out when 1 kg of water cools down by 1 oC is equal to 4.18 kJ.
Which statements are correct about temperature?
I. A rise in temperature of 1.0 oC is the same as a rise in temperature of 1.0 K.
II. Both the degrees Celsius scale and the Kelvin scale are based on the temperature at which pure water melts and boils.
III. Pure water boils at 100 oC and 373 K at 101 kPa (1 atmosphere) pressure.
A rise of 1 oC is the same as a rise of 1 K but the Kelvin scale is absolute and not based on the properties of water. Note that atmospheric pressure is 101.325 kPa whereas standard pressure (i.e. when referring to STP conditions) is 100.000 kPa.
During an experiment to find the enthalpy change for the reaction between zinc and copper sulfate solution a student recorded the temperature of the copper sulfate solution for two minutes. She then added the zinc and continued to record the temperature whilst stirring the solution in the 'coffee cup' calorimeter. She plotted a graph of her data. What value should she use for ΔT when calculating her result?
The graph should be extrapolated back to 2 min (when the zinc was added) to account for heat lost to the surroundings. This gives a value of 27.5 oC. ΔT = 27.5 - 17.0 = 10.5 oC
Which are correct statements about exothermic and endothermic reactions?
I. The bonds in the products are stronger than the bonds in the reactants in endothermic reactions.
II. Both exothermic and endothermic reactions involve the transfer of heat between the system and its surroundings.
III. ΔH has a positive value for endothermic reactions.
The bonds in the reactants are stronger than the bonds in the products for endothermic reactions so more energy needs to be put in than is given out when the bonds in the products are formed.
Which is a correct statement about the enthalpy diagram?
.png)
Absolute values of enthalpy cannot be measured, but the change in enthalpy between reactants and products, ΔH, can.
Which equation represents the standard enthalpy change of combustion of ethane, ΔHc⦵?
The definition is for the combustion of one mole of ethane and the reactants and products must be in their standard states at SATP.
Which equation represents the standard enthalpy change of formation of sodium chloride, ΔHf⦵?
ΔHf⦵ refers to the formation of one mole of the compound from its elements under standard conditions with the reactants and products in their normal states under these conditions.
What mass of ethanol (Mr = 46.1) will need to be burned completely to raise the temperature of 1.00 kg of water by 10.0 K? Assume no heat is lost and that the measurements are made under standard conditions. (ΔHc⦵(ethanol) = − 1367 kJ mol−1; Specific heat capacity of water = 4.18 kJ kg−1 K−1.)
Amount of heat required to raise the temperature of 1.00 kg of water by 10.0 K = 10.0 x 4.18 = 41.8 kJ
1 mol (46.1 g) of ethanol produces 1367 kJ of heat when it combusts completely.
Mass of ethanol required to produce 41.8 kJ = (41.8 ÷1367) x 46.1 = 1.41 g
Which will produce the greatest temperature rise in the resulting solution?
Assume that the both of the initial solutions of sodium hydroxide and hydrochloric acid are at the same temperature.
Work out the limiting reagent to give the maximum amount (in mol) of salt formed and then consider the total final volume. The correct answer produces 0.05 mol of salt in 50 cm3 of solution. When 50.0 cm3 of 2.00 mol dm−3 NaOH(aq) is added to 100.0 cm3 of 2.00 mol dm−3 HCl(aq) the amount of salt formed = 0.10 mol, which is twice as much but the total volume of solution that needs to be heated is now 150 cm3, i.e. three times as much, so the temperature will rise less.
Which has the sign for the enthalpy change different to the other three?
All of them are exothermic except for the ionization energy of potassium.
Twitter
Facebook
LinkedIn