Unit 4 Test: Chemical Thermodynamics

In a calorimeter, 100 g of ice melts at 0°C. The enthalpy of fusion of the ice is 334 J/g. How much heat was absorbed?

33.4 kJ

In a calorimeter, 6.68 kJ of heat was absorbed by 20 g of ice. What is the enthalpy of fusion of the ice?

334 J/g

How much heat do you need to raise the temperature of 150 g of ice from −30°C to −15°C? The specific heat of water is 4.18 J/g°C.

4.61 kJ

Which statement is a correctly written thermochemical equation?

4Fe (s) + 3O2 (g) → 2Fe2O3 (s), ΔH = −3,926 kJ

Which statement is true?

In an exothermic reaction, the energy of the products is less than the energy of the reactants.

In which thermochemical equations would the ΔH be considered a heat of solution?

NH4NO3 (s) → NH4+ (aq) + NO3- (aq), ΔH = +25.7 kJ/mol

200 grams of a substance requires 18.8 kJ of heat to raise its temperature from 25°C to 45°C. What is the identity of the substance?

ammonia

This diagram would represent the enthalpy changes in which example? https://ibb.co/yWh4J1v

hot pack

Which example is an exothermic reaction?

oxidation of iron

Which parameter is kept constant in a coffee-cup calorimeter?

pressure

Which term measures thermal energy in an object?

temperature

You have a series of four chemical reactions 1→2→3→4net. How do you calculate the ΔH2 if you know the other ΔH values?

ΔH2 = ΔH4 − (ΔH1 + ΔH3)

What is likely to be true about the ΔH for this reaction? C6H6 (s) → C6H6 (l)

∆H > 0

Consider these equations: 2S (s) + 3O2 (g) → 2SO3 (g) ΔH = −792 kJ 2S (s) + 2O2 (g) → 2SO2 (g) ΔH = −594 kJ 2SO2 (g) + O2 (g) → 2SO3 (g) ΔH =? What is the missing ΔH?

−198 kJ

How much heat is given off when 16 g liquid methanol (CH3OH) at its freezing point changes to solid methanol? (methanol ΔHfus = 3.16 kJ/mol)

1.58 kJ

A chemical reaction is carried out in a closed container. The energy absorbed by the chemical reaction is 100 kJ. What is the energy liberated from the air or the walls of the container?

100 kJ

The reaction 2NO (g) → N2 (g) + O2 (g) has a ΔH = −180.5 kJ. How much heat will be required to produce 44.8 L of NO by the reverse reaction?

180.5 kJ

Two objects (A and B) of the same temperature are in contact with each other. Which statement is true?

Although the molecules collide, no heat transfers because there is no temperature difference between the objects.

Which type of substance would be best for use in a cooling system?

a liquid with a high specific heat

What is the change in enthalpy when 250 g of water vapor condenses at 100°C? (ΔHvap = 40.67 kJ/mol)

−565 kJ