Chemistry / Chemie - 124
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| For which of the following is DfH° equal to zero at 25°C? | Vir watter van die volgende is die DfH° gelyk aan nul by 25°C? |
| Use Hess’s Law to determine the heat of reaction for the process. | Gebruik Hess se Wet om die reaksiewarmte vir die proses te bepaal. |
Fe2O3(s) → 2 Fe(s) + 3/2 O2(g)
i. 2 Fe(s) + 6 H2O(ℓ) → 2 Fe(OH)3(s) + 3 H2(g) | ΔH° = +321.8 kJii. H2(g) + ½ O2(g) → H2O(ℓ) | ΔH° = -285.8 kJiii. 2 Fe(OH)3(s) → Fe2O3(s) + 3 H2O(ℓ) | ΔH° = -288.6 kJ
| Magnesium pieces (0.492 g) react in dilute acidic solution (134 mL) as follows: | Magnesiumstukke (0.492 g) reageer in verdunde suuroplossing (134 mL) soos volg: |
| Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g) | |
The temperature of the solution increases from 22.2 °C to 44.8 °C. Determine the enthalpy change for the reaction in kJ per mol Mg(s) that reacts. (Assume that the specific heat capacity of the solution, and density of HCl(aq) can be approximated by the values for pure water. Furthermore, no heat energy is exchanged with the calorimeter). | Die temperatuur van die oplossing styg van 22.2 °C tot 44.8 °C. Bepaal die entalpieverandering vir die reaksie in kJ per mol Mg(s) wat reageer. (Neem aan dat die spesifieke hittekapasiteit van die oplossing en die digtheid van HCl(aq) benader kan word deur die waardes vir suiwer water te gebruik. Verder word geen hitte-energie met die kalorimeter uitgeruil nie). |
| What is the resulting temperature when 20 g of water at 88°C is mixed with 21 g of water at 18°C? | Wat is die finale temperatuur as 20 g water by 88°C gemeng word met 21 g water by 18°C? |
When 11 g NaOH dissolves in 249 g of water in a coffee-cup calorimeter, ΔH = −42.6 kJ/mol. The temperature increases from 18.4 °C to X °C. What is the value of X? (Assume that the solution has the same specific heat as liquid water, i.e., 4.18 J/g°C) | Wanneer 11 g NaOH in 249 g van water in 'n koffie-beker kalorimeter opgelos word, is ΔH = −42.6 kJ/mol. Die temperatuur styg van 18.4 °C tot X °C. Wat is die waarde van X? (Aanvaar dat die oplossing dieselfde spesifieke warmte het as vloeibaar water, dit wil sê, 4.18 J/g°C) |
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| If 180.8 J are required to change the temperature of 15.31 g of a substance from 21.1 °C to 31.2 °C, what is the specific heat capacity of the substance? | Indien 180.8 J nodig is om die temperatuur van 15.31 g van 'n stof vanaf 21.1 °C tot 31.2 °C te verander, wat is die spesifieke warmtekapasiteit van die stof? |
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A sample of 2.1 moles of ethanol (C2H5OH) is initially at 20.0 °C. If the sample absorbs 2.8 kJ of heat, determine the final temperature of the ethanol. (Cethanol = 2.46 J g-1 °C-1). | ‘n Monster van 2.1 mol etanol (C2H5OH) is aanvanklik by 20.0 °C. Indien die monster 2.8 kJ warmte absorbeer, bepaal die finale temperatuur van die etanol. (Cetanol = 2.46 J g-1°C-1) |
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| Methanol (CH3OH) is an efficient fuel with a high octane rating. It undergoes combustion as follows: | Metanol (CH3OH) is 'n doeltreffende brandstof met 'n hoë oktaangradering.Dit ondergaan verbranding soos volg: |
| 2 CH3OH (g) + 3 O2 (g) → 2 CO2 (g) + 4 H2O (l) ; ΔH = -1528 kJ | |
| What mass of O2 (g) is consumed when 768 kJ of heat are evolved? | Watter massa O2 (g) word verbruik as 768 kJ warmte ontwikkel word? |
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| Ammonia reacts with oxygen as follows. Determine the enthalpy change (kJ) for the production of 4.70 g of NO2(g). | Ammoniak reageer met suurstof soos volg. Bepaal die entalpieverandering (kJ) vir die produksie van 4.70 g NO2(g). |
4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O(g) ΔH = -1389 kJ
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Hydrazine (N2H4) is a liquid often used as rocket fuel. Upon combustion, it yields nitrogen gas and liquid water. If a 16.6 g sample of N2H4 evolves 1411.2 kJ of heat during combustion, calculate the molar enthalpy change for the combustion of hydrazine? | Hidrasien (N2H4) is 'n vloeistof wat dikwels as vuurpylbrandstof gebruik word. Tydens verbranding lewer N2H4 stikstofgas en water (vloeistoffase). Indien 'n 16.6 g monster van N2H4 1411.2 kJ warmte tydens verbranding ontwikkel, bereken die molêre entalpieverandering vir die verbranding van hidrasien. |
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