Hey guys, can someone please explain this to me:

Consider the following statements about reactions involving enzymes:
I Coenzymes can be metallic ions.
II Coenzymes can accept electrons during a reaction.
III Coenzymes can donate groups of atoms during a reaction.
IV Coenzymes can increase the rate of reaction.
Which of the statements above are correct?
A. I and IV only
B. II and III only
C. I, III and IV only
D. II, III and IV only
How is point IV correct- they dont directly contribute to increasing rate of reactions do they?

Consider an alkaline hydrogen fuel cell.
Which one of the following will reduce the amount of usable energy produced per kilogram of fuel entering
the fuel cell?
A. supplying oxygen in excess
B. increasing the porosity of the cathode
C. reducing the operating temperature from 40 °C to 20 °C
D. reducing the rate at which oxide ions move through the electrolyte

Also How is D wrong for this qs? If oxide ions move more slowly through the electrolyte, wouldn't the production of electricity decrease?

    N1ck3lGall1um Coenzymes can speed reactions up as some enzymes can't bind the substrate without a coenzyme.

    2nd question isn't well written (it examines a specific cell type whereas VCAA says no specific cell required in the study design) although I think the correct answer is C since electrochem is based on equilibrium and if you remove heat, the system will want to generate heat to compensate according to Le Chat's. D can't be right since OH- moves through the electrolyte not O2-

      N1ck3lGall1um

      Yeah that question was weird af.

      You just have to know that, when temperature increases, fuel cells are more efficient.

      Or you can think of it in an energy profile diagram. However, when the temp is higher, it starts higher. (So the ∆H value is higher). Apparently this is wrong (scientifically).... because temperature doesn't effect enthalpy or something... I can't remember.

      Hope this helps 🙂

        Hi! Can anyone here explain why branched alkanes have a lower melting and boiling point? I've been told they have a greater surface area compared to straight chain alkanes but weaker dispersion forces, but I'm sort of confused how that works.

          _sophiestudies_ Linear alkanes are effectively flat and can 'stack' closely together, maximising the dispersion forces between the chains, hence have higher mp and bp's. Branched alkanes cannot get as close together.

            10 days later

            How much heat energy is required to raise the temperature of 250 mL of water from 17 0C to 100 0C? Assume that 1 mL of water has a mass of 1 g and that the specific heat capacity of water is 4.2 J g-1 0C-

            is the answer 87150kj

            also for this question i got
            A solution containing 0.25 g of NaCl dissolved in 50 mL of deionised water will have a concentration ofA. 5.0 gL-1B. 4.3 MC. 5.0 x 10-3 mgL-1D. 2.5 x 10-4 mol/L

            0.086 concentration,i think its wrong could someone help

            and second question
            The sulfate (SO42-) content of a plant fertiliser is to be determined by gravimetrically analysing a 2.5 g sample of fertiliser.
            Question 7 The first part of this analysis would involve
            A. producing a precipitate.
            B. filtering the sulfate ions from the insoluble material in the fertiliser.
            C. dissolving the sulfate from the fertilser into water.
            D. adding an indicator to an aliquot of the sulfate solution.

            Question 8
            An important part of gravimetric analysis is to react the chemical under analysis with an excess solution in order to produce a precipitate. This solution is known as a precipitating reagent. Which precipitating reagent would be the most suitable for this analysis?
            A. NaCl (aq)
            B. Ba(NO3)2 (aq)
            C. KCl (aq)
            D. CuSO4 (aq)

            20 days later

            Hi guys,

            Can electrons only move from the valence shell when in excited state?

            For example:
            Sodium has a ground state electronic configuration of 2, 8, 1.
            Can sodium have an excited state electronic configuration of 1, 8, 2?

            Thank you!

            8 days later

            what is the chemical equation when ethanol is combusted in an excess supply of oxygen?

            for this question in the solutions they have written ethanol as ch3ch2oh, if i wrote c2h6o for ethanol reactant is that fine?

              chemistry1111 Hey, im not too sure if its fine using the molecular formula in vcaa exam, maybe someone can confirm for you. But i personally would not recommend it as a ketone or aldehyde could also have the same molecular formula C2H6O, so i think it is just better to use the semi struc version since its clearer what the molecule is.

                chemistry1111 I think VCAA accepted C2H6O before, but I wouldn't recommend it cuz the molecular formula could be that of an isomer with different functional groups. For fuel definition, I don't think VCAA will ask it, but make sure to allude to the fact that a fuel is a substance with potential energy stored within it (chemical or nuclear) that can be converted to useful forms of energy

                    for question 2 of the 2022 vce exam, why isnt the answer B cause i think solutions i saw said A. could someone explain

                      chemistry1111 that’s cuz you’re not burning water, energy is released by the fuel to heat its surroundings (in this case, H2O)

                        Does anyone know how to do this

                        Propane burns completely in oxygen according to the equation:
                        C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
                        The amount of energy released per tonne of
                        carbon dioxide produced is determined to be
                        1.68 × 104 MJ t–1.
                        Determine the ΔH value, in kJ mol–1, for the thermochemical equation. (1 tonne = 106 g)

                          a month later

                          snowflake
                          Combusting 1 tonne of C3H8 releases 1.68 × 104 MJ

                          So the question is, how much energy does combusting 1 mol of C3H8 release?

                          So first you need to convert 1 tonne into mol:
                          1 tonne = 1 000 000 grams
                          n = m/M (n = number of moles, m = mass, M = molar mass)
                          M (C3H8) = 3 x 12 + 8 x 1 = 44 g/mol
                          n = 1 000 000 / 44 = 22727 mol

                          So if combusting 22727 mol of C3H8 releases 1.68 × 104 MJ, combusting 1 mol would release (1.68 x 104)/22727 MJ = 0.7392 MJ = 0.7392 x 1000 kJ = 739.2 kJ

                          Therefore, the ΔH value, in kJ mol–1, for the thermochemical equation is 739 kJ/mol.

                            9 days later

                            is there a difference between petrodiesel and petroleum gas or are they the same thing?

                              mia46789

                              Hi, yes there is a difference. Petrodiesel is 25% aromatic hydrocarbons and 75% alkanes which are in the C10H22-C15H32 range. Petroleum gas, on the other hand, is composed of much shorter alkanes, mainly propane (C3H8) and butane (C4H10).

                              Another difference is that petrodiesel is a liquid, whereas petroleum gas, as the name suggests, is a gas, though it is usually stored under high pressures making it liquid petroleum gas (LPG).

                              Both are usually obtained from crude oil.

                                  GreenAcorn I agree with the above, it's usually safe to assume that petrodiesel is dodecane (C12H26) and petroleum gas is propane. Likewise, you can assume petrol is octane