Questions tagged [temperature]

A measure of the average kinetic energy of the particles in a sample of matter; may be expressed either in kelvin (symbol K) or in degree Celsius (symbol °C).

Filter by
Sorted by
Tagged with
8
votes
3answers
2k views

Temperature of an atom

I read somewhere that the temperature of an atom is not defined. The definition of temperature is only for larger systems. Why is this so?
8
votes
1answer
862 views

What determines humidity limit / dew point of the air? - Why can air only hold a certain amount of water?

From Wikipedia: The dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. At ...
7
votes
2answers
2k views

What is an example of a very low temperature endothermic reaction?

Shakashiri describes the reaction of solid Ammonium Thiocyanate and solid Barium Hydroxide Octahydrate resulting in an endothermic reaction leading to subzero temperatures. I've performed this ...
8
votes
2answers
3k views

What causes the colour when conducting flame tests on solid salts?

The normal technique for flame tests is to dip a clean nichrome or platinum wire into a solution of the relevant salt, and observe the resulting flame colour when inserting the wire into a non-...
4
votes
2answers
358 views

Why does a liquids height in a Barometer depend linearly on pressure?

Here is a derivation I found relating the pressure P, gravity g, height h, and density $\rho$, of a liquid in a barometer $$ P=\frac{mg}{A}\\ V=Ah \\ P = \frac{mgh}{V}\\ \rho=\frac{m}{V}\\ P = \rho g ...
5
votes
3answers
493 views

What value of temperature does T represent in Gibbs Free Energy Equation?

Temperature before, or after reaction? Temperature change? Or what is it?
2
votes
1answer
826 views

how to use di-tert-butyl dicarbonate (diBOc) as a solvent?

how should we use di-tert-butyl dicarbonate(diBOc) as solvent? In reference, diBOc was in the form of a liquid but when I checked the bottle it was in solid state. diBOc should be stored at 8-10 ℃. ...
6
votes
1answer
93 views

What are the physical properties affected in ZnO when there is a sulfur impurity?

I have a question. I work at a brass metal foundry where one of our waste products is $\ce{ZnO}$, which we sell. Because we have been making new alloys which contain sulfur, our $\ce{ZnO}$ has a very ...
6
votes
2answers
5k views

Are there two compound resins that tolerate over 1000°C for glass/carbon fiber?

I'm a hobby enthusiast that loves to play with electronics so my major is not in chemistry, there for I'm hoping that this forum is the right place to find aid in this question. I've searched day in ...
2
votes
1answer
2k views

Does the density of a liquid and gas phase of a substance(nitrogen or water) converge when reaching critical point

I know that the there is no difference in density in a liquid and a gas phase of a substance after the critical point. But I do want to know if this difference in density is more continuous or if it ...
2
votes
1answer
198 views

Density of water and temperature

Is there a formula that shows how the density of water is affected by temperature? For example, with the speed of sound it can be shown how temperature will affect the speed: $$V = 331\ \mathrm{m/...
1
vote
1answer
161 views

Can we define a new unit instead of specific heat that is constant with temperature rise?

Specific heat plays an important role in calculating energy and thus, heat, enthalpy and etc. But as I sighted the definition for calorie, I was surprised. A calorie is the amount of heat needed ...
5
votes
1answer
1k views

Why do some solid chemicals dissolve better in colder water?

I just discovered that some solid chemicals, such as $\ce{Na2SO4}$, dissolve better in cold water than hot water from here and would like to know if there is any particular reason as to why. Is it ...
-4
votes
2answers
161 views

When will the mass of the reactant increase while being heated up?

Thermo-gravimetrc analysis, often refered to as TGA, measures the mass of an unknown solid substance as it heats up, of course for the elemental analysis of the very substance. When the substance is ...
0
votes
1answer
82 views

Effect on kinetic energy of a body with change in temperature

Why doesn’t the energy of a body doubles when temperature in degrees Celsius is doubled? I know that it doubles in case of kelvin scale.
0
votes
1answer
146 views

Can I change viscosity of an HDPE polymer?

I want to make composite with HDPE and wood, but when I melt it I have problem to mix them, because this polymer have high viscosity.
8
votes
4answers
39k views

How are hot and cold defined?

My teacher asked me this question a few days ago. "How to define hot and cold?" And I said, "The higher the temperature, the hotter you are. The lower the temperature the colder you are." But my ...
0
votes
1answer
1k views

Difference between the absolute thermodynamic scale and ITS-90

What is the difference between the absolute thermodynamic temperature scale and the practical temperature scale: ITS-90?
1
vote
2answers
13k views

Effect of temperature on equilibrium

Why is exothermic reactions are favoured by low temperature while endothermic reactions are favoured by high temperature?
0
votes
1answer
23k views

Finding the equilibrium temperature between two substances in a constant pressure calorimeter

I need to find the temperature two things equilibrate to in a constant pressure calorimeter given only their specific heats, masses, and starting temps. The only thing I know for specific heat is ...
6
votes
3answers
21k views

Determining weight-percent methanol in water from specific gravity and temperature

The company I'm working with uses a fuel mixture of methanol and water. We use a hydrometer to measure specific gravity, in order to test the composition of fuel received from our suppliers. To ...
3
votes
2answers
24k views

Derivation of the relation between temperature and pressure for an irreversible adiabatic expansion

I have a formula for finding the final temperature in an irreversible adiabatic expansion. $$T_2=\left[\frac{C_v+(\frac{P_2}{P_1})}{C_p}\right]T_1$$ where $T_1$ is the initial temperature. $C_v$ and $...
3
votes
3answers
842 views

Why won't increasing the temperature increase the solubility of a gas in a liquid solvent?

If I raise the temperature of a solution of a gas in a liquid solvent, why won't the solubility increase? Increasing the pressure will increase the solubility, but increasing the pressure doesn't ...
3
votes
1answer
110 views

Residual stress in polymer coatings

A paper talks about the residual stress when coating polymers. It says that residual stress is the sum of the "heat stress" (due to the difference in thermal expansion coefficients) and the "shrinkage ...
0
votes
2answers
2k views

Determining boiling point on a created temperature scale

1.Assume that you construct a thermometer using gallium as the fluid instead of mercury, and that you define the melting point of gallium as 0 °G and the boiling point of gallium as 1000 °G. What is ...
12
votes
2answers
378 views

Why no thermal expansion for camping tents?

I know that solid materials expand when heated, which is called thermal expansion. But what is happening to tent square or tent canvas of (plastic?) camping tents? I have noticed, that during the day,...
1
vote
1answer
1k views

Why do all medicines require storage temperatures below 25 °C?

Almost all medicines I buy have storage requirements saying $T\le25^\circ C$. But do they really spoil at higher temperatures? What if they are stored at e.g. $30^\circ C$, which is common at ...
2
votes
2answers
4k views

Henry's Law with varying temperature

I am trying to determine what the derived partial pressure would be for CO2 in the global atmosphere from historical inconstant temperatures and CO2 concentrations of the global atmosphere: Is it ...
3
votes
2answers
688 views

Plot of Arrhenius Equation with temperature

I saw the following plot of the Arrhenius Equation on Wikipedia (cc-by Zivilverteidigung and Matthias M.). It is a concave upwards graph, but according to the equation $$k= A \mathrm e^\frac{-E_\...
11
votes
2answers
12k views

What is the reason for anomalous expansion of water?

What is the reason for anomalous expansion of water? Why doesn’t it simply expand on heating or contract on cooling? Why it shows anomalous behavior at 4 degrees Celsius? Why not on 4.6 or 10 (or ...
1
vote
1answer
115 views

Behaviour of water at exactly 0 °C

If I had a beaker of water (i.e. many molecules), at exactly 0 °C and at atmospheric pressure, what phase would be encountered? And would the answer to this also apply to other substances at their ...
6
votes
1answer
139 views

How can I reduce Crystallization temperature of seed oil to be used in winter as biodiesel?

How can I reduce Crystallisation temperature of seed oil to be used in winter as biodiesel? The glycerol has been removed from the oil, and white spirit is used to reduce its viscosity.
0
votes
2answers
188 views

Generally available fluid with good heat transport properties

I have designed a container which is heated up and has to heat up some tube-coils of water inside of it. This container is filled with a fluid that can help store and transfer the heat received from ...
5
votes
2answers
15k views

How to judge if a reaction is exothermic or endothermic

Mix $\ce{HCl}$ and $\ce{NaOH}$ together (reactants are at the same temperature) in a calorimeter. The temperature increases, and the book says it's an exothermic reaction. I don't get it. The ...
2
votes
1answer
68k views

How do I find the final temperature using specific heat?

What is the final temperature of water and iron if a $30~\mathrm{g}$ piece of iron at $144~\mathrm{°C}$ was dropped into a calorimeter with $40~\mathrm{g}$ of water at $20~\mathrm{°C}$? Specific heat ...
2
votes
1answer
63 views

How does the process of protein denaturatation work?

I know it's the proteins that somehow change their properties at some temparature. But what kind of change, in terms of molecule-level structure?
1
vote
2answers
2k views

Given the volumes: determine the pH and the final temperature of a mixture knowing only the initial pH and the temperature of the un-mixed components

I have a pretty basic question but the last time I took Chemistry was in 2007. I am studying the Navy's Nuclear study guide for their interviews and one of the question I am faced with is below. ...
1
vote
1answer
224 views

Change in pressure or volume of molten salt

I am doing a project in which I fill a cylinder with a volume of $636cm^2$ (made of stainless steel) with molten salt: 60% Sodium Nitrate ($NaNO_3$) and 40% Potassium Nitrate($KNO_3$). The container ...
5
votes
1answer
89 views

What is the term for the amount of volume change at a phase boundary?

Apologies for the extremely basic question, but I would like to look up the amount by which the volume (or equivalently, density) of various substances changes when they freeze. However, I don't know ...
1
vote
1answer
181 views

How to increase the velocity of a reaction?

I'm doing relatively simple Chemistry but I've been given a formula for the velocity of a reaction. $$v= k \cdot c_\mathrm A^a$$ and $$k= A \cdot \mathrm e^{E_\mathrm a/RT}$$ As a result, from ...
3
votes
1answer
529 views

Temperature in the Maxwell-Boltzmann Distribution

I am attempting to generate the probability for the specific speed of a molecule using the Maxwell-Boltzmann distribution, but I cannot decide on which temperature I should use in the equation. For ...
2
votes
3answers
4k views

Dry ice and acetone

In my organic chemistry class there are several reactions that I’ve been told are generally conducted at $\pu{−78^\circ C}$, which is apparently also the temperature of dry ice in acetone. This is ...
1
vote
2answers
17k views

Heat Produced when Mg is reacted with HCL

Calculate the heat produced when a strip of $\ce{Mg}$ metal with a mass of $0.0801$ gram is reacted with $50.0$ml of $1.0M$ $\ce{HCl}$ to raise the temperature of water to $7.6^\circ C$ (change in ...
0
votes
2answers
1k views

how to increase Keq(equilibrium) with temperatrue

$$\ce{C_{(s)} + H_2O_{(g)} <=> CO_{(g)} + H_{2(g)}}$$ $$\Delta H = +131\ \mathrm{kJ}$$ If the reaction is in a state of equilibrium under standard conditions, what can be done to increase ...
23
votes
2answers
53k views

Why does water evaporate at room temperature?

When water temperature reaches $100\ ^\circ \mathrm{C}$, the molecules get so excited that the hydrogen atoms lose the bonds to the oxygen atom and therefore the water starts to become gas. I get that,...
4
votes
1answer
3k views

Does the bond dissociation enthalpy vary with temperature?

The $\ce{H-H}$ bond enthalpy is $436 \mathrm{kJ/mol}$: $$\ce{H2 (g) -> 2H (g)} \qquad \Delta H = +436 \mathrm{kJ/mol}$$ Does this only apply at the standard temperature of $298 \text{K}$, i.e. ...
3
votes
2answers
602 views

does Sodium persulfate evaporate at room temperature

I use Sodium persulfate to etch a copper board to manufacture home made Printed Circuit Board (PCB), and I use the same etching tank on the below photo which has no cover on the top. I wonder if it is ...
5
votes
2answers
861 views

Is sublimation caused by an environmental difference or an element's composition?

I was having a conversation when the topic of sublimation came up. Prior to the discussion, I had always thought that sublimation was caused by a great pressure/temperature difference, but another ...
4
votes
2answers
1k views

Chemical Equilibrium - Why does changing the temperature shift the equilibrium?

I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side. I know that $\Delta G = \Delta H − T\Delta S $ but I don't know how to ...
1
vote
0answers
34 views

Chemical Equilibrium - Why does changing the temperature shift the equilibrium? [duplicate]

I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side. I know that $\Delta G = \Delta H - T \Delta S$ but I don't know how to ...