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

Dalton's Law of Partial Pressures Calculator

Calculates the partial pressure of each gas in a mixture: P_i = x_i · P_total, and the total pressure as the sum of up t...

basic

11,093 4.0 1 min

Chemistry

Graham's Law of Effusion Calculator

Compute the ratio of effusion (or diffusion) rates of two gases at the same temperature and pressure using Graham's law:...

basic

24,504 4.8 1 min

Finance / Investing

Treynor Ratio Portfolio Beta Return Calculator

Calculates the Treynor ratio using portfolio return, risk-free rate, and portfolio beta to measure reward per unit of ma...

basic

2,438 4.0 1 min

Chemistry

Second-Order Integrated Rate Law Calculator

Solves the integrated second-order rate law: 1/[A]_t = 1/[A]₀ + k·t. Given any three of the four variables ([A]₀, [A]_t,...

basic

8,341 4.0 1 min

Physics

Planet Equilibrium Temperature Calculator

Compute a planet's blackbody equilibrium temperature T_eq = T_star · √(R_star / 2d) · (1 − A)^(¼) given the host-star te...

basic

20,706 4.3 1 min

Chemistry / Reactions

Activation Energy (Two-Temperature) Calculator

Compute the activation energy Ea from rate constants k₁ and k₂ measured at temperatures T₁ and T₂ using the integrated A...

basic

8,434 3.8 1 min

Finance

Contribution Margin Per Unit Calculator

Computes the contribution margin per unit (CM = selling price − variable cost per unit) and the contribution margin rati...

basic

11,467 5.0 1 min

Chemistry

Gas Stoichiometry: Volume from Moles at STP Calculator

Compute the volume occupied by a given number of moles of an ideal gas at standard temperature and pressure (STP): V = n...

basic

14,803 4.5 1 min

Chemistry

Mole Fraction from Mass Composition Calculator

Converts mass composition of a binary mixture into mole fractions from component masses and molar masses.

basic

1,646 4.4 1 min

Physics / Mechanics

Coefficient of Restitution from Pre/Post-Collision Velocities Calculator

Compute the dimensionless coefficient of restitution e (a measure of energy lost in a collision) from the pre- and post-...

basic

13,300 4.6 1 min

Everyday Life

Smartphone Battery Charge Time Calculator

Estimates smartphone or device charging time from battery capacity (mAh), charger wattage, current charge level, and cha...

basic

14,209 5.0 1 min

Physics / Mechanics

Projectile Maximum Height from Launch Angle and Speed Calculator

Compute the apex height a projectile reaches when launched at speed v₀ and angle θ above flat ground (no air resistance)...

basic

12,026 4.2 1 min

Showing 85 to 96 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

Dalton's Law of Partial Pressures Calculator

Graham's Law of Effusion Calculator

Treynor Ratio Portfolio Beta Return Calculator

Second-Order Integrated Rate Law Calculator

Planet Equilibrium Temperature Calculator

Activation Energy (Two-Temperature) Calculator

Contribution Margin Per Unit Calculator

Gas Stoichiometry: Volume from Moles at STP Calculator

Mole Fraction from Mass Composition Calculator

Coefficient of Restitution from Pre/Post-Collision Velocities Calculator

Smartphone Battery Charge Time Calculator

Projectile Maximum Height from Launch Angle and Speed Calculator

Reviewed by Dr. Helena Ortiz

Equilibrium Constant Calculator

Length Converter

Combined Gas Law Calculator

Capacitance Calculator

pOH Calculator

Carbon Footprint Calculator