Tijuan mixed a solid and a liquid together in a beaker. he determined that a chemical change occurred.
if his conclusion is correct, which substances could he have been observing and why?
ice mixed into warm oil, because the change of state that occurred when the ice melted cannot be reversed
baking soda mixed into vinegar, because the production of bubbles indicates that a new substance formed
sugar mixed into hot water, because the disappearance of solid indicates that the chemical identity of the sugar changed
sand mixed into water, because when sand was added the mass of the beaker increased

second option, baking soda mixed into vinegar, because the production of bubbles indicates that a new substance formed.

Explanation:

1) Indeed the evolution of bubbles when two different substances are mixed together is a good indication that a new substance has been formed. That is because the bubbles are a gas product of the chemical reaction between the reactants.

2) Since, baking soda (NaHCO₃) and vinegar (acetic acid, CH₃COOH) are aqueous solutions, you do not have bubles evolving when they are not mixed. Once, they are mixed, the acetate ion (CH₃COO⁻) will combine with the sodium ion (Na⁺) forming sodium acetate (CH₃COONa) and CO₂ which is the gas (bubbles).

3) Regarding the other options:

i) ice mixed into warm oil: the melting of the ice is just a change of phase, and that is all what you can tell about this interaction. Certainly not a chemical change. In fact, that change can be easily reversed by cooling the mixture.

ii) sugar mixed into hot water: the disappearance of the solid sugar does not indicate that the chemical identity of the sugar changed; it just dissolved; a solution was formed. If you heat the solution, the water will evaporate and you will be able to see the sugar crystals.

4) sand mixed into water: this is a classical example of a heterogeneous mixture, where both substances remain clearly being the same. The addition of mass is not an indicator of a reaction. Mass conservation is a principle that is valid for both physical and chemical changes.

answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.