how is temperature related to the physical change of a substance?

What is correlation between temperature and pH? Does high temperature tend to decrease the pH?

In thermophilic anaerobic digester, the pH is lower than mesophilic AD at the end of the culture. Is there any reason for it?

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Dar es Salaam Institute of Technology

Probably the increased temperature is commonly associated with the dissociation of water molecules resulting to more concentration of the solution hence more acidic due to increased free H ions in solution

All Answers (31)

National Geophysical Research Institute

pH is defined as negative logerethem of hydrogen ion concentration. It varies from 1 to 14. I to 6.9 is acidic and 7.1 to 14 alkaline.. 1 is highest acidic and 14 is highest alkaline. 7 is neutral, pH is measured by specific sensors/electrodes and in room temperature along with proper calibrations.Therefore when pH measured at room temperature there is no direct correlation between pH and temperature.

New York University Abu Dhabi

The below link says that pH is decreasing slightly with increase in temperature.

you can also refer to the below link:

National Geophysical Research Institute

pH can be defined as the chemical potential (mu) divided by thermal energy (kT). Hence pH is proportional to the chemical potential due to H+ concentration reduced by kT. If, for a given system, the ratio of mu/kT remains constant with temperature, pH is expected to be independent of temperature. Otherwise, pH could change accordingly.

National Geophysical Research Institute

You are correct Mohammad Ghatee. I appreciate your finding.

Your are quite well-come Virendra Saxena

Aalborg University - Esberg

In a strictly chemical sense, the hydrolysis (H2O = H+ + OH-) constant is temperature dependent. Neutral pH is 7 at 25C and about 6 at 100C. The controls on pH are rather more complex in your. Other chemical reactions from waste products are temperature dependent as well, but it sounds like you have different reaction products (anaerobic and mesophilic AD) and that the specific biological reactions and their byproducts are probably the important factor. Can't really say anything more without more details.

BMT Construction and Investment J.S.C.

In fact, pH is defined as the concentration of proton H+, so it depends on this concentration. If we have a system, in which the concentration changes when changing temperature, of course pH will change. Some system can produce proton H+ when increasing temperature, so the pH value will decrease. On the contrary it increases, The answer depends on the physical chemistry process of detail system.

Yes, pH is related to the temperature. Recently my work on aluminuim dross also found that different salt cake (one type of solid wastes from aluminuim industry) have different response of pH to temperature. In my cases, heat is released in the process of reaction of aluminuim dross with water, and the differences of pH in landfill ( high temperature) and the pH in the laboratory can be more than 1 unit difference. I think that it is mportant for us to pay attention of the realtion of pH and temperature for the wates managements.

Another point need to be clear is that pH is related to activity of proton H+, not the concentration, There were many observations for the pH and temperature. Here is one of the examples, released at 1945 in Biochem, It is observed that pH were dropped in the sodium Carbonate-bicarbonate Buffer solutions when temperature increased ( e.g. room temperature to 37oC).,

Centre for Cellular and Molecular Biology

Dawood University of Engineering and Technology Karachi

The neutral value of pH changes with change in temperature. Following is important references on the subject

Akiya, N. and P. E. Savage (2002). "Roles of Water for Chemical Reactions in High-Temperature Water." Chemical Reviews 102(8): 2725-2750.

National Geophysical Research Institute

Aquil, your problem is very much interesting but sofisticated. However it can not be generalised. Kindly go through :

The effect of temperature on pH measurement

Authour Jhon, J., Barron Colin, Ashton & Leo Geary, Technical Service Department Reageon Dagonestic LTd. Shannon Free Zone, County, Ireland.

is it also happen on food? that pH dropped when temperature increased

University of Asia Pacific

pH is changed when temperature is increased because pH is a simplified way to numerically quantify the H+ ion concentration of a given solution. Increasing in temperature also increasing the molecular vibration of concentration of [H+] ion for this decrease tendency of forming hydrogen bonds, thus leading to reduction in pH. So to ultimate pH in inversly proportional to temperature.

Recently we published a paper titled "Why Does pH Increase with CaCl2 as Draw Solution" (doi:10.1016/j.psep.2016.06.007) (http://authors.elsevier.com/sd/article/S0957582016300933).

We found that the pHs of both NaCl and Na2CO3 increased with concentration while the pH of CaCl2 decreased with concentration.

This shows that charges on salts affect their solution pH. Positive charges contributes to lower pH and negative charges increase pH.

In anaerobic digesters, more cations (Zn2+, Cu2+, Ca2+, Fe3+) will be leached out at higher temperature (thermophilic) and the pH becomes lower (Positive charges contribute to lower pH).

If we heat CaCl2 solution, I guess pH of the solution will increase because of the pH of water. I haven't done the experiments. You could try if interested.

Karlsruhe Institute of Technology

Have a look on the solution-pH vs. Temperature graph in the following link:

pH in inversly proportional to temperature. With an increase in temperature more energy is there for molecular vibrations and consequently water molecules fall apart more easily. Therefore, the equilibrium concentration of H+ rises, causing the pH of water get decreased with rise in temperature.

The other observation is that with increase in temperature the rate of photosynthesis increases which may increase pH value and the alkalinity of water increases. Hence one will find a positive correlation. Earlier I expressed opposite view. The matter is not so simple. The final decision maker is nature, the ecosystem! Start working with real life situation and get the data, analyze it with statistical tool. You will get your answer yourself!

National Institute of Oceanography and Fisheries

you may see this paper I hope it helps you

Explanation:

We write the autoprotolysis of water as:

H2O⇌H++OH−

Kw is quoted at 298K and is equal to 10−14, so as you know the equilibrium should lie strongly to the left. Since the extent of reaction is so small, we would be justified in saying that this is an endothermic reaction.

Another way to look at it is to consider that it is a bond-breaking reaction that requires energy to break a strong O−H bond. Given that it is a bond-breaking reaction, increase of temperature would probably drive the reaction further to the right, and result in greater concentrations of H+. Since, by definition, pH=−log10{H+}, pH should indeed decrease at higher temperature.

National Institute of Technology, Durgapur

The formation of hydrogen ions (hydroxonium ions) and hydroxide ions from water is an endothermic process. Using the simpler version of the equilibrium:

H2O(l)⇌H+(aq) + OH−(aq)

Hence, the forward reaction, as written, "absorbs heat".

According to Le Châtelier's Principle, if you make a change to the conditions of a reaction in dynamic equilibrium, the position of equilibrium moves to counter the change you have made. Hence, if you increase the temperature of the water, the equilibrium will move to lower the temperature again. It will do that by absorbing the extra heat. That means that the forward reaction will be favored, and more hydrogen ions and hydroxide ions will be formed. Therefore the concentration of H+ ions counts to increase which in turns reduce the pH of the solution as pH=−log10[H+].

For more details look into the page

With my pH meter Horiba F23 :

Compensate pH with temperature :

pH(x)= pH(t)-∂(t-x) , ∂=0.02pH/oC

pH( x) : at sampling point , pH ( t) at measuring at lab .

So if temp increase , pH will increase too.

Karlsruhe Institute of Technology

I am not chemist, but this is my understanding of change of pH with temperature:

As stated in the link below, "the change in solution pH with temperature is controlled by the temperature-dependent dissociation constants. The effect of temperature on solution pH increases as the pH approaches the dissociation constant. For strong acids and bases, the dissociation constants are beyond the 0 to 14 pH range, so the primary effect is the water dissociation constant that is 1 x 10-14 at 25°C. Consequently, the effect of temperature is substantial for basic solutions" (see figure in https://www.isa.org/standards-and-publications/isa-publications/intech-magazine/2009/december/web-exclusive-opportunities-for-smart-wireless-ph-conductivity-measurements/ )

The change of pH with temperature is very trivial for neutral water (e.g. from pH 7 at 25 °C to pH 7.47 at 0 °C). In addition, this does not mean that water becomes more alkaline at lower temperatures because in the case of pure water and according to the Le Châtelier's principle there are always the same concentration of hydrogen and hydroxide ions and hence, the water is still neutral (pH = pOH) even if its pH changes. The pH 7.47 at 0°C is simply the new reference of neutral water pH at 0 °C.

Florida Atlantic University

Conductivity means the amount of electricity a substance of unit mass and area allows passing through it however, there is no relation between pH and conductivity, as pH is related to the number of hydrogen ions per molecule of an acid/base and conductivity depends on free electrons.

Conductivity is directly proportional to with Temperature. While the pH is inversely. proportional . The pH value of a solution is directly dependent on the temperature. A pH value without a temperature value is incoherent. pH decreases with increase in temperature. But this does not mean that water becomes more acidic at higher temperatures. A solution is considered as acidic if there is an excess of hydrogen ions over hydroxide ions. In the case of pure water, there are always the same concentration of hydrogen ions and hydroxide ions and hence, the water is still neutral (even if its pH changes). At 100°C, a pH value of 6.14 is the new neutral point on the pH scale at this higher temperature. [H+] also increases due to a decreased tendency of forming Hyderogen bonds, thus leading to a reduction in the pH.

But some time conductivity also increases when the pH increases, but slower. And there is a conductivity minimum at neutral pH.

Hi Prem Baboo

Basically, the conductivity of a mixture or pure substance depends on the free electron or charged particle ready to transfer the electric charges. In this regard, the strong electrolytes are the strong conductor of electric charge and weak electrolytes are weak conductors. From this viewpoint, one expects to see a weak electrical conductivity from a buffer solution, which is composed of a weak acid or a weak base and its corresponding salt in water, having a specific pH. The relation between pH and electrical conductivity could b a complex one.

Institute of Microbiology of the Czech Academy of Sciences

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Federal Urdu University of Arts, Science and Technology

Soluble metals form hydroxide in water which increase pH at low-temperature solubility decrease and concentration of hydroxide decrease which decrease pH, while in high-temperature solubility increase and a large amount of hydroxide form which increase pH.

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