Featured contributor PhD Applied Physics; former research associate at a national metrology lab.

Dr. Helena Ortiz

Senior Reviewer, Science & Engineering

0 calculators 0 articles Member since Jun 2026

About

Helena is the senior technical reviewer for physics, chemistry, and unit-conversion calculators. She is the last pair of eyes on every formula — checking constants, units, and edge cases against primary sources and standards bodies.

She holds a PhD in Applied Physics and previously held a research post at a national metrology lab.

Areas of expertise

Physics Chemistry Unit conversion Measurement standards

Education & credentials

BSc Physics — Universidad Complutense de Madrid
PhD Applied Physics — Stanford University

Chemistry

Equilibrium Constant from Gibbs Free Energy Calculator

Compute the thermodynamic equilibrium constant K from a reaction's standard Gibbs free energy change ΔG° (kJ/mol) at tem...

basic

15,253 3.9 1 min

Chemistry / Solutions

Cryoscopy: Molar Mass from Freezing Point Depression Calculator

Determines the molar mass of an unknown solute from the measured freezing point depression: M = Kf × w_solute(g) / (ΔTf...

basic

17,966 4.1 1 min

Statistics / Descriptive

Sample Variance and Standard Deviation from Summary Stats Calculator

Calculates sample variance s² = [Σx² − (Σx)²/n] / (n−1) and sample standard deviation s = √s² from the sum of squares, s...

basic

17,190 4.4 1 min

Physics

Fick's First Law Diffusion Flux Calculator

Compute the steady-state diffusive molar flux J (mol·m⁻²·s⁻¹) across a region of concentration gradient dC/dx (mol·m⁻⁴)...

basic

24,957 4.4 1 min

Chemistry

First-Order Reaction Half-Life Calculator

Compute the half-life of a first-order reaction directly from its rate constant: t½ = ln 2 / k = 0.693 / k. The half-lif...

basic

4,518 4.3 1 min

Physics / Mechanics

de Broglie Wavelength Calculator

Compute the de Broglie wavelength of a moving particle from its mass and speed, using λ = h / (m · v) with h = 6.626 × 1...

basic

3,196 4.7 1 min

Chemistry

Density of an Ideal Mixture from Mass Fractions and Component Densities Calculator

Compute the bulk density of an ideal liquid mixture from up to three components, each given as a mass fraction (decimal,...

basic

4,162 3.8 1 min

Chemistry

RMS Speed of a Gas Molecule from Temperature Calculator

Compute the root-mean-square speed of a gas molecule at temperature T from kinetic theory: v_rms = √(3·R·T / M), where R...

basic

24,851 4.5 1 min

Finance

Interest Tax Shield from Interest Expense and Tax Rate Calculator

Compute the annual interest tax shield — the value of deductibility of interest on debt: tax shield = interest expense ×...

basic

2,545 4.1 1 min

Chemistry

pH of a Buffer After Strong-Acid Addition Calculator

Compute the new pH of a Henderson-Hasselbalch buffer after adding moles of a strong acid (HCl). The strong acid converts...

basic

17,005 4.0 1 min

Chemistry / Solutions

Effective Osmolality from Serum Glucose and Urea Calculator

Calculates serum osmolality: Osm = 2×[Na⁺] + glucose(mg/dL)/18 + BUN(mg/dL)/2.8. Effective osmolality (tonicity) exclude...

basic

21,709 4.6 1 min

Physics / Mechanics

Standing-Wave Fundamental Frequency on a String Calculator

Compute the fundamental frequency f₁ and the first two overtones of a stretched string fixed at both ends from the strin...

basic

16,271 4.1 1 min

Showing 181 to 192 of 504 results

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Reviewed by Dr. Helena Ortiz

These calculators were technically reviewed by Dr. Helena Ortiz for accuracy.

Chemistry / Reactions

Equilibrium Constant Calculator

Compute the equilibrium constant K_c from the concentrations of two products (with stoichiometric coefficients 1) divide...

basic

5,060 4.0 1 min

Conversions / Length

Length Converter

Convert between meters, kilometers, miles, feet, inches, and yards.

Featured basic

4,964 4.2 1 min

Chemistry / Solutions

Combined Gas Law Calculator

Find the missing pressure, volume, or temperature using the combined gas law for a fixed amount of gas.

basic

5,360 4.2 1 min

Physics / Electricity

Capacitance Calculator

Compute the capacitance of a parallel-plate capacitor from plate area, plate separation, and the dielectric constant.

basic

12,524 4.1 1 min

Chemistry / Solutions

pOH Calculator

Compute pOH from hydroxide ion concentration and the matching pH at 25 °C.

basic

18,221 4.2 1 min

Ecology / Carbon Footprint

Carbon Footprint Calculator

Estimate your annual personal CO₂e footprint from home energy, driving, flying, and diet — with adjustable emission fact...

Featured basic

15,825 4.9 1 min

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Dr. Helena Ortiz

Equilibrium Constant from Gibbs Free Energy Calculator

Cryoscopy: Molar Mass from Freezing Point Depression Calculator

Sample Variance and Standard Deviation from Summary Stats Calculator

Fick's First Law Diffusion Flux Calculator

First-Order Reaction Half-Life Calculator

de Broglie Wavelength Calculator

Density of an Ideal Mixture from Mass Fractions and Component Densities Calculator

RMS Speed of a Gas Molecule from Temperature Calculator

Interest Tax Shield from Interest Expense and Tax Rate Calculator

pH of a Buffer After Strong-Acid Addition Calculator

Effective Osmolality from Serum Glucose and Urea Calculator

Standing-Wave Fundamental Frequency on a String Calculator

Reviewed by Dr. Helena Ortiz

Equilibrium Constant Calculator

Length Converter

Combined Gas Law Calculator

Capacitance Calculator

pOH Calculator

Carbon Footprint Calculator